Often people are reluctant to give away items that they perceive as valuable.
"I know I never wear those shoes, but they cost me $200!"
The value trap is a double bind; there is a practical component and an emotional one.
First, you may think your stuff is worth a lot of money, but it's likely that you're just thinking about what you paid for it. You spent $200 on those cute sling-backs, but would someone else give you $200 for them today? Things are only worth what someone is currently willing to pay for them.
Second, you are wrapping more and more negative energy around this thing that you don't really want. You hesitate to discard something you spent $200 on, but never wore. That feels like throwing money straight into the trash. But guess what? You are never getting that $200 back. Just accept that this was not a fabulously great investments and MOVE ON. Otherwise you have to feel that guilt, shame, and annoyance every single time you see those shoes. That doesn't seem like a good use of your precious energy.
Here are just a few things, expensive when new, that do not generally retain their value: clothing, sports equipment, electronics, of-the-moment collectibles, anything to do with a baby. Try to be realistic about the actual cash value of the things you own. Check out Craigslist or other online sellers and see what other people are asking for similar items. Ugh. Those shoes are only going for $20 today, and apparently no one else found them comfortable, because there are 15 pairs already available on Ebay.
Maybe you find that the thing you don't want really is worth money. So, are you going to get out there and sell it? If you are determined to do it, I recommend setting a time limit. You don't want that rowing machine anymore, but you've been complaining about how it cost too much to toss. Give yourself two weeks to put it on Craigslist or take it to a consignment store. If the two weeks pass and you haven't gotten around to it, donate it. Let someone else enjoy that thing you hate. Donating something valuable to a worthy non-profit or a friendly neighbor is an excellent way to take advantage of that item's worth. You get to feel good about your action, and you get the added advantage of never tripping over that stupid machine again.
The beauty of letting go of things that are bound up with negative emotions is that you get to let the bad feelings go as well. Now when you look in your closet you won't have that twinge of guilt about the shoes you shouldn't have purchased in the first place. Peace. That's what this is all about.