This is a great question. While it's unclear how we will value rare assets (like a one-of-a-kind painting) with tokens, ultimately the market will decide the value.

Since you like analogies, here's an analogy using the stock market. If investors buy a stock in a company, and never hear anything from the company again, they'll lose faith in the company, everyone will sell, and the value of the stock -- and thus the company -- will go down.

It's likely the same thing will happen with tokens: if someone buys a token backed by a Warhol painting, but Warhol starts to go out of style, the value will likely go down. If there's a Warhol renaissance, or MOMA puts on a huge Warhol retrospective, the value will go up.

Thus, tokens will motivate the owners of the underlying asset to always be ADDING VALUE, just as the stock market motivates corporate managers to constantly ADD VALUE with their companies. Hope that helps!