Why do people sell their cryptos when their value starts to drop a bit??

I suppose they don't want losses, but instead of panicking and selling, they should just convert to USDT so their investment would be safe.

We could also agree that a crypto, for example BNB, increases its value to a certain point (e.g., 700 BNB) and then convert to USDT and make it drop in value (e.g., 650 BNB) and convert again, so many of us would win 😄