You've hit on a corner stone of the human condition: we can't fully appreciate how much something means to us until it's gone. I don't know if this will help you or not but my work-arounds for this are 1) try to imagine where you'll be in 5 or 10 years and anticipate what things you'll miss about the present when you're at that future point.
The other is to flip the whole thing on its head by leaning into negativity bias and sparing a thought for all the ways things could be worse, but aren't. Like, I'm pretty stoked my legs still work, because someday they probably won't. I mean, that can only get you so far since you only know how much something means after you've lost it, but at least it's something.
If this isn't helpful, at least consider yourself in good company.
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