Agreed on the technical problems- the "hard" problems in my career have been massive degradations/failures with no error messages, which are typically solved with liberal application of strace, gdb/pdb, iproute2/ss and Wireshark. Once you find the smoking gun in the kernel or on the wire then it becomes simple again.

I guess the hardest problems I've ever "solved" (mitigated) were mental (depression/anxiety/impostor syndrome). But those aren't one and done happy endings- they're a bundle of general anxieties that are never fully resolved. You just learn how to manage.