Webster's Revised Unabridged Dictionary · 1913

hindsight

hindsight , noun

understanding the nature of an event after it has happened; as, hindsight is always clearer than foresight.
Collocations (1)
20-20 hindsight or twenty-twenty hindsight , Perfect understanding of an event after it has happened; -- a term usually used with sarcasm in response to criticism of one's decision, implying that the critic is unfairly judging the wisdom of the decision in light of information that was not available when the decision was made.