Some people argue writers' block doesn't exist, that it's an excuse and you should tough things out. Sound familiar? A bit like exercise in the gym?
I think writers' block is like pain. It's a warning sign.
When my novel freezes on me and I'm sitting at the computer typing s-l-o-w-l-y, and then, deleting, the chances are I've written myself into a blind alley. Usually (because I have problems being nasty to my characters) the issue is I've skipped over or avoided a conflict that I should have developed and explored. Create and harvest tension. When things are dragging, I get writers' block. It's my pain signal--probably designed to save the reader from boredom :)
One final point. Writers' block can be a sign your energy is going somewhere else--into fighting an illness, dealing with personal issues, taking up a cause. Although I wish otherwise, our energy has limits. If you want to write, you have to prioritise your writing. Sometimes there is good reason your writing comes second, but then, you can't beat yourself up about writers' block.