(I think I'm reading this the right way but if not feel free to correct).
In a word: pain.
Until there's a legitimate threat to their well-being (emotional, psychological, or financial), the lessons won't be truly "learned." Until you know the true cost of a decision, you're flying high.
Older engineers have dealt with this organically so it's kind of encoded into their DNA. The very reason certain things aren't done (or a certain way) is because that pain has already been felt/encouraged learning a better way.