It's just stuff.
The last move was about a year ago and I've been downsizing ever since. I'd rather be doing anything else - which is why it took so long. Spring cleaning was a real reward because there was less to deal with. I jettisoned furniture, books, clothes and collectibles going from a 2400 to 750 square foot house.
Honing an attitude about how material stuff really doesn't matter helps with downsizing. I can't say I personally felt that way, but I'm sure it does help. Just because you can't take it with you to heaven, or wherever, doesn't mean you can't cram it into the shed now. It may just be stuff but it's your stuff. George Carlin comes to mind: That's all your house is - a place to keep your stuff while you go out and get more stuff.
The urge to purge is much weaker than the desire to acquire. Thinking of it as pulling weeds in the garden to give remaining plants more strength helps with the item thinning. I can't say I personally thought of it that way, but I'm sure it does help. I gripped tightly to huge chunky antique furniture and piles of dishware that I knew wouldn't fit in my tiny house and paid to move it twice before giving it away.
Property is theft. Nobody “owns” anything. When you die, it all stays here. (101 Greatest George Carlin Quotes.)