The demo is the beginning
A demo answers whether a system can work once. A product must answer a different question: can it keep working when the inputs are untidy, attention is scarce, and nobody is watching?
Reliability is not polish applied after the interesting work. It is the interesting work. Each repeated use reveals another assumption the original model hid.
What survives
I now look for boring evidence: recovery after interruption, understandable failure states, and outcomes that remain useful after the novelty disappears. The best systems earn trust quietly.