In addition to the advice here already (some of which I agree with, some not), here are two other ideas:

1. Ask yourself WHY you’re keeping it? Does the explanation hold water?
2. Work through one area at a time, and do multiple cycles. It’s easier to work on a single room or area at a time, and if you can purge a modest amount easily, then you can work through the whole house like this. Then you go back for a second pass and will probably have a more critical eye for getting rid of stuff - another 15% goes from each room in turn.