speculation & deduction in the past

This is something we may find it difficult to "come to terms with". Let's think of songs that could help here.

The first one I can think of is Pretty Woman OST "It must've been love"

Then I think of "When I was your man" by Bruno Mars

or "I should have known better" by The Beatles

or "I should have known better" by Jim Diamond

or "I could have danced all night" from My fair lady 

And all the ones you feel like sharing ....