A person willing to ask “what am I missing?” becomes harder to fool.

Asking what you are missing is the single most protective question available. Nearly every deception, whether by someone else or by your own reasoning, works by keeping something out of view, and the habit of explicitly looking for the missing piece disrupts that more reliably than suspicion does.

Build it into anything significant: a deal, a decision, an account that seems clear. Ask what would have to be true for this to be a mistake, and what has not been mentioned. Then go looking for that thing specifically. It is a small ritual that catches a large share of avoidable errors.