The approach many courses take to physics, specially "modern Physics" is really bad, this is how it should be taught:
- start by describing experiments that the previous best theory did not explain. This gets intimately entangled with basically learning the history of physics, which is extremely beneficial as also highlighted by ron Maimon.
- then, give the final formula for the next best theory
- then, give all the important final implications of that formula, and how it amazingly describes the experiments
- then, give some mathematical intuition on the formulas, and how the main equation could have been derived
- finally, then and only then, start deriving the outcomes of the main formula in detail
This is likely because at some point, experiments get more and more complicated, and so people are tempted to say "this is the truth" instead of "this is why we think this is the truth", which is much harder.
But we can't be lazy, there is no replacement to the why.