[yomritoyj]

This is not necessarily a wrong thing to teach. As one progresses from old things that are well-understood to new developments,students will have to deal with fuzziness and gaps. They must learn to make progress using a heuristic feel for the subject instead of complete rigour. Too sensitive an alarm for missing foundations will actually stop them from being productive. Think of how much time passed between the invention of calculus and the development of rigorous analysis.

[jessriedel]

That's probably appropriate for quickly progressing fields, but not for fundamental physics which has utterly stagnated. People wasting time on important but nearly intractable topics certainly happens (e.g., arguably myself on quantum foundations). But this is absolutely dwarfed by the number of researchers eager to springboard to a cutting edge, which hasn't moved much in decades, but who remain ignorant of the basics.

The terrible incentives for professors to quickly make graduate students useful, rather than invest in fundamental understanding that won't pay off for many years after they graduate, should also lead us to suspect the correct balance isn't being struck.