Fixed bets, expensive mistakes
Because bets are small individually, people call too much. Over many streets, 'one more bet' becomes a full stack of mistakes.
Folding a non-nut low when the nut low is out is a skill. Calling because 'it's only one bet' is how limit players go broke slowly.
Track one session: every time you think 'it's only one bet,' write it down. Add them up after. That sum is the tuition fee for passive calling.
Track 'only one bet' lines. Sum them. That's the tuition fee.