Let’s say You like a book, you spend lot of time reading it , you really enjoyed the flow of the story, you can literally feel the smile litting up your face on mention of the book. But that story had unexpected sad ending. Same story which made you smile some time back ,left you alone with tears. Now when you think of it again , even those happy moments haunt you badly . But being the loyal reader, you visit your bookshelf and look at it with teary eyes. You don’t dare to pick it up again and read or forget about it.
Now coming back to your question, our past is like this book, which you might have enjoyed but can’t bring it back again to relive . Because you know now how things will end, it’s time is gone. Present is waiting eargerly to get your attention. Try to live in present for a change.