Hindsight, the knowledge and understanding that you have about an event only after it has happened.
e.g. " I knew in hindsight I shouldn't have put my red shirt in the wash with my white one".
Hindsight simply means, 'looking back on a situation or event after it has happened. Usually used in the idiom 'hindsight is always 20/20" Meaning you can see things more clearly when you look into the past than when experiencing things in the present.