Respect yourself enough to act correctly even when nobody could prove otherwise.

Behaving well when detection is impossible is really a transaction with yourself. There is no external return, and the only thing produced is your own regard for yourself, which turns out to matter more than most external rewards. People who have this tend to be steadier, and it is not mysterious why.

Find the situation where you could act badly with no consequence at all and act correctly anyway. Do not tell anyone. The absence of an audience is the entire value of the exercise, because it makes clear that the standard is yours rather than borrowed from whoever might be watching.