The word "怪不得" is formed through a conceptual fusion where the character "怪" (to blame) is combined with "不得" (cannot, not permitted) to create a new, unified meaning. It literally begins as the idea of "cannot blame", but through habitual use, this literal sequence transforms into a single expression of sudden understanding or realization. The formation effectively compresses a mini-logical deduction, "since this is the case, it is not right to blame or be surprised", into a compact term used to signify that something now makes sense in light of new information.