The map is not the territory. Validating against anything other than the actual feature is a lossy proxy. It may be an acceptable tradeoff because building the feature is too costly but that’s the whole discussion at hand.
I like this metaphor. Looking at a map, we may get a pretty good understanding of whether it's a place we'd like to spend time, say, on vacation.
We don't physically go to a place to scrutinize it.
And we don't limit ourselves to maps only. We check reviews, ask friends, and what have you. We do cheap validation before committing to a costly decision.
If we planned vacations the way we build software products, we'd just go there (because the map is not the territory), learn that the place sucks, and then we'd complain that finding good vacation spots is costly and time-consuming. Oh, and we'd mention that traveling is a bottleneck in finding good spots.
How many dinners a day can you have?
You would still rely on alternative proxies, like recommendations or reviews.