This is such an interesting thread to me. I started becoming uncomfortable with clutter and excess, partially by watching as my parents grow older, all the stuff that gets in their way of enjoying life. That and the occasional binge-watch of "Hoarders" on a rainy Sunday morning.
I started streamlining my bag and clothing stash last year without any real method, then read the KonMari book and was suddenly inspired. So I went through my closet and got rid of everything (almost) that I didn't love. When it came to bags, I did feel guilt, but it was more about realizing that, for example, the $1200 I spent on that Chloe bag that I almost never use,, and could never recover my $$ from, could have gone towards something more meaningful. That realization really pushed me over the edge, and I got much more aggressive in my selling off of things, coupled with the fact that the initial outlay of cash for items no longer used to their potential, really is a completely sunk cost. ANYTHING I get for it is a bonus, and this freed me up to get rid of a lot. The upside? Between eBay, consignment, and selling off scraps of gold (from adjustments, broken pieces, etc), I'm much freer than I was in January and I have a nice little chunk of cash that I will be much more careful about spending. This is really found money, no matter how small or large it may be, or how little of a % I got from the re-sale. As a result, I now have zero guilt about getting rid of these things, only guilt (and a lesson) of how not to repeat that.
I want to use this lesson I learned to apply to future purchases. It's easy to justify a spend on things that are somewhat frivolous (I really didn't need that Chloe bag, just convinced myself I did) when you don't need the $$ for something else, but such a regret when you do need it and it isn't there, or you are trying to be more mindful of spending on timeless things.