Semi-related anecdote: when I was choosing between several grad school offers in math and physics, I visited a couple of top institutions, and at one math department I told the department chair about my dilemma of whether to continue in (pure) math or theoretical physics. I was basically told: look, if you graduate with a math PhD you'll likely find an assistant professor position right away, whereas if you graduate with a theoretical physics PhD you'll likely be looking at at least two terms of postdoc (assuming you're successful in both cases, that is). (I chose physics in the end.) There was one of the first instances of ideal clashing with reality for me.