Idiom: something in the past cannot be fixed, so it must be forgiven

When you are very sad, hopeless and depressed, you let things slide (= you fail to give things the attention they needed).

I agree with Wozitoya. "to let it slide" means "to make an exception" or "to forgive", whether it can be fixed or not.

hi "to let slide" means "to let go", "to drop it"... depending the context...

To let it slide means to let it go...to not hold on (to the problem anymore). I hope that helps! :)