Most NFTs are like a title to a house. Like a title to a house, you can:
1. Prove you own it;
2. Sell it to someone.
Unlike the title to a house:
1. The party certifying your ownership is not the government, but the consensus rules of a blockchain;
2. The thing you own is not physical, but digital in nature;
3. Your ownership does not prevent anyone from copying the file itself for their own uses.
Regarding your point that the object you own might not be consistent: because of the cost relative of storing data on a blockchain, the actual digital thing you own isn't usually stored on the blockchain, but a hash of that file (e.g. [1]). Unless hashing is broken, this is cryptographic proof that the object does remain consistent.
Most NFTs are like a title to a house. Like a title to a house, you can: 1. Prove you own it; 2. Sell it to someone.
Unlike the title to a house: 1. The party certifying your ownership is not the government, but the consensus rules of a blockchain; 2. The thing you own is not physical, but digital in nature; 3. Your ownership does not prevent anyone from copying the file itself for their own uses.
Regarding your point that the object you own might not be consistent: because of the cost relative of storing data on a blockchain, the actual digital thing you own isn't usually stored on the blockchain, but a hash of that file (e.g. [1]). Unless hashing is broken, this is cryptographic proof that the object does remain consistent.
[1] https://github.com/larvalabs/cryptopunks/blob/master/contrac...
Edit: perhaps the notion of an entry ticket to a concert would have been a better analogy than a title to a house.