I'm purging my closet (again) and I think I've figured out why this can be such a challenge. Two reasons, really. For me, anyway, and I imagine a number of other people.
1. Happy Memories - Some clothes remind me of times past when I wore them and the great memories that accompany those particular times. Ergo, wearing them again will bring fun and happy times. Rather a false conclusion, but I found myself reminiscing about a variety of good memories. It's great that I have those memories, but keeping extra clothes in my closet which I no longer wear isn't producing more wonderful life experiences. So they have to go. If I feel that attached, I could always take a picture of the item. But then I'd be cluttering up my hard drive. Just be happy with the memories and photos I already have and move on.
2. Expectations - Then there are those clothes which almost fit and surely they will fit...as soon as I drop a few (or more) pounds. This is just ridiculous. If I am actively losing weight right this moment and may possibly be able to wear an item in the next few months...then maybe they would be worth taking up space. But the reality is that I'm not. I'd like to be. I want to be. But until I actually am? Fuhggetaboutit. Let them go. Buy new clothes if/when I lose the weight. Much better to have the free closet real estate and potential shopping later, anyway.
Having these two explanations helped me. A lot. I will admit that I hung onto a few more items than I probably should, but if I haven't worn them by the end of the season (switched out winter for summer), then they can go to a better home this fall. In the meantime, I have breathing room in both my half closets, which makes me very happy.
The clothes squished on the right hadn't been gone through at this point. Interestingly, they represent how crowded this space was, all mashed and wrinkled together. The clothes on the left are an equal number, but given some space. Much better.