Very hard to say without a specific situation.

For example, if I lie to my partner about being unfaithful to him, then I am betraying him twice - infidelity plus lying about it. But if I don't tell my friend's husband that she is being unfaithful to him, I've done nothing wrong because I should not be involving myself in someone else's relationship. That's a boundary issue so I should keep my mouth shut. Just one example.

My mother does not respect my boundaries so I frequently withhold info from her. That's my right. On occasion I might even make something up just to get her off the phone or avoid talking at all...."I've got to run an errand now" when really I just want her to leave me alone. One is not telling and one is a lie but neither one is "damaging."