Yes, and gas fees for failed transactions ensure you can’t just take unlimited shots at it either. However, if you are monitoring the markets and your code, connections to the network, etc. are fast enough, you can make a fortune using flash loans. A few days ago I found a trade where someone made $17k on a single trade [1] with the only necessary capital being a ~$170 transaction fee. They took a $250k flash loan that they successfully arbitraged. Smaller amounts are made all day every day.

[1] https://etherscan.io/tx/0xfd35e99cbbefea68874391a14ddb09a289...