  We investigate student comfort with the material in an upper-division
spins-first quantum mechanics course. Pre-lecture surveys probing students'
comfort were administered weekly, in which students assigned themselves a
"discomfort level" on a scale of 0--10 and provided a written explanation for
their choice. The weekly class-wide average discomfort level was effectively
constant over the semester, suggesting that the class found no single unit
especially jarring nor especially easy. Student written responses were coded
according to their reported source of discomfort---math, math-physics
connection, physics, and notation. The relative prevalence of these categories
varied significantly over the semester, indicating that students find that
different units present different challenges, and also that some of these
challenges fade in importance as the semester progresses. Semi-structured
interviews with students in a similar quantum mechanics course at a different
institution provided additional context and insight into these results.
