1. On-chain financial freedom?

Today is Da Hei's 100th day in the crypto circle. He has earned some from airdrops and made a small profit on DEX, feeling very confident. That day, he saw a message: 'The XYZ project just launched on Uniswap, the community is super hot, private sale cost $0.02, current price is only $0.05, reaching $0.2 is not a dream!' His heart raced: isn't this the ticket to his 'on-chain financial freedom'?

2. Sharp vision, enter early, and wait for the doubling?

He immediately opened Uniswap and entered the contract address. Sure enough, the pool was just created, with TVL of less than $100,000, and the buy orders hadn't piled up yet. He prepared to enter with 0.8 ETH, thinking it would be too late once others discovered. He silently recited: 'I have sharp vision, enter early, and wait for the doubling.' Considering this was a front-running operation, Da Hei cleverly raised the Gas Price by two notches, confidently clicking Swap. The wallet prompted a slippage setting of 5%. He thought for a moment, this project is highly volatile, so he simply adjusted it to 10%. The faster, the steadier. What’s there to fear? I’m here to make quick money!

3. Huh? Half less

The transaction was confirmed. But when he opened his wallet, he was instantly stunned. He expected to buy 0.8 ETH for 16,000 XYZ, but actually received only 8,600! He was dumbfounded: 'Why is it suddenly half less?? Did I click the wrong thing?'

3. Sandwich Attack

He hurried to check the transaction record on Uniswap. The price instantly rose from 0.05 to 0.095, then back to 0.06.
And his transaction was completed right in the middle of this range. Checking the block explorer, he found he was sandwiched between two faster transactions: one was a high Gas front-running buy, the other was a high Gas immediate sell. In short:
📍 Your transaction is first broadcast to the mempool
📍 Bots target you and use higher Gas to 'cut in line' for a 'front-run buy'
📍 Once you buy, they immediately 'sell' for arbitrage

You think you are 'rushing fast', but in reality, you are the 'target of precision calculation' by others, this is a Sandwich Attack.

5. Mindset collapsed

Da Hei didn't just lose on slippage this time, but also on mindset: he watched his Token's market cap shrink by 40%. At first, he thought it was 'high price volatility', and later realized that he wasn't 'buying the wrong project', but was systematically harvested.

What's even scarier is that all this is done automatically. MEV Bots monitor the mempool around the clock, and once they detect 'large amounts + high slippage' transactions, they immediately execute the sandwich strategy. Many bots are even competing for this 'retail opportunity'. On-chain, there are not only hunters but also wars between hunters.

Da Hei's mindset completely collapsed. He shared the transaction record in a Telegram group, and a group member immediately recognized: 'You got sandwiched, buddy. Next time, try using Flashbots protection.' He then realized that there were 'invisible channels' to prevent transactions from being monitored in the mempool.

6. Give everyone a hint

After this lesson, Da Hei made several decisions:

✅ For any new coins rushing the early market, strictly control slippage to not exceed 1%
✅ For trades over 0.5 ETH, split orders + simulate pricing
✅ Commonly used MEV protection plugins/aggregators (CowSwap, Flashbots Protect)
✅ Always remind yourself: On-chain transparency ≠ safety

Da Hei took this lesson to heart and updated his trading notes: 'I didn't buy high, I was sandwiched.'
Blockchain is transparent and open, information is symmetric, but power is asymmetric. It's not that you're stupid, but that others are too fast, too knowledgeable, and too ruthless.

Alright, the story is over, now it's knowledge point time:

First, we need to understand: in the on-chain world, there is no real novice protection. It is both a free market and a dark forest. If you don't go to hunter school, you are prey. Da Hei is just one of many retail investors, but this time, he learned how to pick up the telescope and put down the fantasy.

📌 Small knowledge extension: What is MEV?

MEV = Maximal Extractable Value
Refers to block producers or bots extracting value from traders by sorting, inserting, rejecting transactions, etc. Sandwich Attack is just one of them, others include:

  • Front-running

  • Liquidation sniping

  • Token sniping

📌 How to prevent being harvested by MEV bots?

✅ Use private paths like Flashbots Protect, CowSwap
✅ Control slippage (try not to exceed 1% for large amounts)
✅ Split orders, trade in batches
✅ Use simulators or monitoring tools to assess price impact in advance
✅ Avoid major event nodes (launching, announcements, airdrops)