the.com/benefit of the doubt

means Choosing to believe the better, more charitable explanation for someone's action when you can't be sure which explanation is true.

from Built from 'benefit' (advantage, favor) plus 'doubt' — the phrase emerged in legal and moral English as shorthand for the idea that uncertainty should tip in favor of the accused rather than against them, echoing the older legal principle that it's better to risk acquitting the guilty than convicting the innocent. Over time it slid out of courtrooms into everyday speech, where it just means choosing trust over suspicion when the facts won't settle the matter for you.