So AirTag isn't for items I'm likely to lose, it's for items I'm not likely to lose because they're always attached to me, meaning I'd sense their absence immediately...
It is for items that could
get lost / misplaced. In a general sense things likes keys, luggage, backpacks, wallets etc. do get left behind (or in the case of luggage "lost")
I know people who have misplaced keys inside their own house. They were left in a pants or jacket pocket, in the clothes hamper, etc.
Obviously there are people who are very perceptive / organized so they'd be more aware. There are just as many people (or more) who leave or misplace things. It seems so unlikely that a person wouldn't notice, but it happens.
A look at any "Lost & Found" section at a mall, theme park, hotel, movie theater, etc. shows there are a TON
of lost and forgotten items.
I lost my car keys at at AMC once. It was during a cooler season, so I wore a jacket & at some point during the movie my keys fell out of my jacket pocket (Reclining seats + loud movie explosions apparently made it easy for them to fall out of my pocket with me knowing it). By the time I got to my car I realized I didn't have them, but we had made a few stops at other shops, so in a panic, we had to retrace our steps.
For me, it's more of a (cheap) additional level of protection. I always put AirTags in my luggage when I travel, so if my luggage gets left behind / lost. It makes it easier to show the airline rep where it is (And it definitely works in those regards)
My goal is to NOT have to use AirTags (because that means I misplaced something) but I have them in the event I need them.