# MEV - The Invisible Hand in Your Pocket

**Published by:** [Lista DAO](https://blog.lista.org/)
**Published on:** 2026-07-13
**URL:** https://blog.lista.org/mev-the-invisible-hand-in-your-pocket

## Content

I lost three dollars on Sunday. I want to be clear that this is not very much money. By the standards of the kinds of stories Moolah had been hinting at - the billion-dollar hacks and the weekend implosions - three dollars is rounding error. By the standards of the lesson I learned from losing it, three dollars was a bargain. I would, looking back, have paid more. But I want you to feel what I felt at the time. Because the part nobody tells you about being sandwich-attacked is that, while it's happening, you don't know it's happening. The trade goes through. The number you receive is slightly worse than the number you expected. You shrug and assume it was slippage and move on. Which is exactly what the bots are counting on. Most people never even know they were robbed. I was about to. We were at the kissaten. Moolah had asked me to bring fifty dollars in USDC and to sit with my phone in front of me, ready to swap. She had picked the trade - fifty USDC for a token I had never heard of, a small one with thin liquidity. She had picked it deliberately. "Set the slippage to ten percent," she said. "Keep it loose. We want to see what happens." "What's going to happen?" "You'll find out. Press swap when I tell you. Not yet." She looked at her phone. She watched something. Dev was leaning over her shoulder watching the same thing - a website I couldn't see clearly. After a moment Moolah looked up. "Now." I pressed swap. The transaction went through in about ten seconds. The amount of the small token I received was, on first glance, about what I had expected. The price had moved a little. Within my one-percent slippage tolerance. Nothing seemed wrong. "Did it work?" I asked. "Yes. Now - look at the transaction on the block explorer. I want to show you what happened around your trade." She opened the page. There were three transactions, in order, all in the same block: A trade buying the token. A larger amount. My trade. Smaller. A trade selling the token. The same larger amount. "Tell me what you're seeing," Moolah said. I stared at the screen. "Someone bought the token right before me." "Yes." "And then sold it right after me." "Yes. The same address. Bought, then waited for your trade, then sold." "Why?" "Because of how the pool works. Remember the buckets? When someone makes a large buy, the price in the bucket moves up. When someone makes a large sell, the price moves down. The bot saw your transaction - before it happened - sitting in a public waiting room called the mempool. The bot saw your fifty dollars about to land. It calculated: if I buy first, I push the price up; her trade then pushes it up further; I sell into the higher price she just created. The bot bought, your trade went through at a slightly worse price than it would have otherwise, and then the bot sold for a small profit. The price of the token returned to roughly where it had been. The bot pocketed the spread." I looked at the three transactions in the block. "How much did the bot make?" "About four dollars. Of that, about three dollars came from you. Your trade got a slightly worse fill than it would have if you had been alone in the pool. That worse fill is the bot's profit. They didn't reach into your wallet. They simply made the price you got worse, by an amount they captured for themselves. You paid the difference. You did not know you were paying it. Most people never do." I sat with this for a minute. "This is called a sandwich attack," Moolah said quietly. "Your trade is the meat. The bot's two trades - buy before, sell after - are the bread. You are squeezed in between them. The pool is the same pool you were going to use anyway. The bot did not break anything. It simply saw your transaction first and acted on the information." "How is that legal?" "There is no law against it on the blockchain, unlike its counterpart in traditional finance. The blockchain has no laws, only rules. The rule is: anyone can submit a transaction, and the order in which transactions appear in a block is determined by who pays the most in fees to whoever is building the block. The bot saw your trade in the mempool, paid a slightly higher fee, and got placed in front of you. Then it paid another slightly higher fee for the second trade, to be placed right after you. The block builder - the validator who assembled the block - collected those fees. Everyone followed the rules. You, simply, were not in the room when the rules were being followed." I wrote in the notebook, slowly. Mempool = public waiting room of pending transactions. Bots watch. Sandwich attack = bot front-runs, then back-runs. "There is a name for this whole category," Moolah went on. "Miner's Extractable Value. MEV. It refers to all the value that block builders can extract by choosing the order of transactions in their blocks. It also goes by another name with the same abbreviation: Maximal Extractable Value. It includes sandwich attacks, but also: arbitrage - closing price differences between exchanges, which is generally considered benign. Liquidations - being the first to liquidate an unhealthy lending position, which is necessary for the system to function. Front-running - buying ahead of a known large order. The category is huge. Some MEV activities are good. Some are neutral. Some are predatory." "How much MEV is extracted per year?" "Last year, on Ethereum alone, somewhere around eight hundred million dollars by some estimates. There are entire teams of engineers whose job is to extract MEV. There are entire teams of engineers whose job is to avoid MEV being extracted from their users. There is, in some sense, a constant invisible war happening underneath every single transaction in DeFi. You only see the result. The result is that most retail trades are slightly worse than they would otherwise be. The skim is small but constant." "Is there protection?" "Yes. Several kinds. Some wallets and aggregators now route transactions through private mempools - instead of broadcasting your trade publicly, they send it directly to a block builder under a confidential agreement that the builder won't sandwich it. The transaction never enters the public waiting room. The bots never see it. They cannot front-run what they cannot see. There are services called Flashbots Protect, MEV Blocker, others - all variations on the same idea. Tighter slippage - setting point one percent or two percent - limits how badly a sandwich can hurt you, because if the bot's manipulation pushes the price past your tolerance, your trade simply fails. Sometimes the wallet you use will pick a quiet moment, or split your trade into smaller pieces. The countermeasures are evolving. The arms race continues." "What should I do?" "For small trades, on quiet pools, you'll mostly be fine. The bots aren't profitable on tiny amounts. For larger trades, on thin pools - like the one we just used - protect yourself. Use a private mempool. Use a tight slippage. Use a major aggregator that has MEV protection built in. Or trade on a Layer 2 where the MEV economics are different, sometimes better." I looked at the three transactions on the screen one more time. The bot's address. My address. The bot's address again. The neat, almost surgical way the trade had been wrapped around mine. There was something specifically humiliating about it. Not because the amount was large - it wasn't - but because I had been completely unaware. I had pressed swap. I had received my tokens. I had thought everything was fine. And in the meantime, somewhere on a server in a country I have never visited, a piece of software I will never see had taken three dollars off my trade and added it to its own balance, and would, by the end of that day, have done the same to ten thousand other people. "Have you ever read the essay called Ethereum is a Dark Forest?" Moolah asked. "No." "You should. It was written by a man named Dan Robinson. He compared the public mempool to a dark forest at night. You can hear creatures moving but you cannot see them. The moment you reveal your position - by sending a transaction into the mempool - you are seen by every predator in the forest. The good ones ignore you. The bad ones pounce. The forest is not malicious. The forest is simply a forest. The predators are simply predators. To survive, you either move quietly - through private mempools - or you accept that the predators will take their share." "That's a bleak metaphor." "It is the metaphor that has stuck most among the people who think hardest about this. Because it is accurate. The blockchain is not a friendly place. It is a place where the rules are public and the predators are profit-seeking and the forest does not care whether you live or die." I closed the notebook for a moment. The senbei on the kissaten table was untouched. Outside the window, the snow was finally - finally - starting to melt. The first true thaw of the year. "I'm sorry you lost three dollars," Moolah said gently. "I wanted you to feel it once, with my supervision, in an amount that did not hurt you. Most people who learn this lesson learn it on a trade much larger, and they never even notice. You will, from now on, notice." I would. I do. I have not made an unprotected swap on a thin pool since. Next: Derivatives On-Chain

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