So you might ask why should I lend my crypto out while the price is high and get paid back when it's low, well I will tell you why you should do that.
In the long run, if you lend out 1 bitcoin while it's $10,000 and you get paid back the $10,000 while bitcoin is $9000 and it after goes back up above $10,000 you would have made over $1000. Then you say what if the price just goes up? well then you will have in the first place made the deal that he will pay a full bitcoin no matter if it hits $13,000 or $20,000 so either way, it's really just a win-win for you in the end.
If you want a more secure way to lend you could always sign up for Coinloan and lend out your FIAT or crypto at the same time get collateral so your investment always will be safe in case they can't pay you back. Sign up to Coinloan to learn more about how you can earn more from your money by lending.
Now yes you kinda do the same when you sell high buy low, but here you are a little more safe in case you miss selling very high if you ask me. You won't lose anything if it goes up or down and you can earn a lot if it goes down in price and back up.