If you hold ETH and USDC in your Metamask wallet (an asset "Pool"), you "Pool Ratio" will change simply because of ETH price change. You don't "lose" anything extra from this.
Consider the following Scenario:
Number of ETH
Number of USDC
Once this is understood, we can start to talk about what else would cause the Pool Ratio to change.
Our LP pool is a lot like a Chinese Hot Pot where you have two soup flavors (here, I attached a picture), one soup flavor is called LINK, the other called ETH. Because this is a magical pot, LINK soup can be converted to ETH soup and vice versa. And as long as the conversion rate (price) is fair, the overall pot is still full of good soup. This is what happens when we deal with most traders: a few come in for some LINK soup and take out some ETH soup; and the next few do the opposite. Yes, of course, sometimes you have more LINK soup and sometimes more ETH soup, but these are all fair conversions. This is called "Cyclical Imbalance". Oh don't forget, you get to charge a fee for providing this conversion service.
The problem here is with toxic traders: they steal soup from you, period. And as more and more of them come through, you have less and less soup. They do that by "front-running". The key pillar of "front-running" is that they know what you don't 100 milliseconds ahead of time. It's almost entirely about a time advantage. So our counter-move also has to do with time: anyone who wants to buy soup, place your order now, but you must WAIT 5 minutes before you get your soup. They lose their time advantage, they lose their edge, and our soup pot is safe again. This is why we have a "Trade Delay".