To protect your valuable money in the world of DEX, you must understand MEV - a simple explanation (As always, there are omissions and exaggerations for simplicity) Have you ever had a strange experience where you swapped to buy a meme coin on DEX, but received far fewer tokens than expected? It's not a bug or an error. The validators have taken your money. MEV (Maximum Extractable Value) is, as the acronym suggests, when validators "extract the maximum value" from transactions. There are various types of MEV, but the most problematic is the sandwich attack on transactions. Let's assume you have 100 $SOL and are swapping it for $TRUMP. (Let's assume the price at this point is 100 SOL = 1000 TRUMP) 1. The validator receives the swap transaction of 100 SOL -> TRUMP. 2. Just before executing this transaction, the validator inserts a transaction to swap 100 SOL -> 1000 TRUMP first. 3. Since the validator's transaction is executed first, the price of TRUMP has increased, and the original transaction is swapped for 950 TRUMP instead of 1000 TRUMP. At this point, the price ratio is 100 SOL -> 900 TRUMP. 4. Now your swap is executed, and TRUMP becomes even more expensive, right? Then the validator swaps the 1000 TRUMP they just bought back for 110 SOL. In other words, the validator makes a profit of 10 SOL by effectively taking advantage of your swap transaction. The order in which transactions are included in blocks and executed is at the discretion of the validators, allowing them to maximize profits through MEV. In this process, users of the network incur losses, which is why MEV is sometimes referred to as an "invisible tax." So, should you just accept this? There are ways to protect yourself. The easiest method is to set a "slippage" limit. When using a DEX, you can usually find an option to set slippage. Slippage is the percentage that allows you to cancel a transaction if the requested price differs from the actual execution price. In other words, the higher you set this slippage, the more likely your transaction will become a tasty meal for the validators. In fact, MEV is not entirely bad. Unlike sandwich attacks, it can also maximize profits through arbitrage between different DEXs, improving network efficiency and potentially increasing staking yields. Therefore, we need to block MEV that harms users, like sandwich attacks, while allowing beneficial MEV that benefits the entire network to be executed more efficiently. Recently, the trading volume on DEX in Solana has surpassed that of many CEXs. In Ethereum, MEV has been a problem for a long time, and various solutions (like sharing MEV profits when sent to a specific RPC) have emerged. However, in Solana, MEV has quietly been an area where validators and JITO have been profiting. As trading volume increases, MEV will likely become a more significant issue in Solana, and various infrastructures will be developed to address it. [Summary] If you don't want to get completely wiped out by validators when using DEX, make sure to set your slippage properly.