The best proof of a thing being viable is you built it and it worked.

But if you can project forward thought experiments with deep relevant intuition you can avoid mistakes.

The thought experiment only works if you have relevant knowhow, and you don't project out too far.

If the idea you're considering fails the thought experiment, it most likely doesn't work. But if it passes the thought experiment, it might work.

So thought experiments are best for finding paths that don't work and pruning them.