A project creates useful resistance
It is easy to understand a principle when nothing pushes back. A real project supplies the missing resistance: incomplete information, awkward edge cases, time limits and people who do not behave like the diagram.
That resistance turns knowledge into judgement.
Build the smallest honest version
The smallest useful prototype is not always the one with the fewest screens. It is the one that preserves the important uncertainty. If the question is about trust, a technically impressive mock-up with no meaningful privacy decisions may be smaller but it is not honest.
Keep the lesson portable
I try to finish an experiment with one or two ideas I can carry elsewhere. The code may belong to a particular project; the judgement should travel.