"(1) An accurate mental model of how the program should behave, with sufficient detail to hypothesize about why it's not behaving that way" -- While working as a firmware engineer, I once got a bug from a customer, he reported that they were in Argentina and the device with the firmware would lose an hour in the time displayed every time they had a power loss and that the problem goes away when they put the time-zone to Brazil, this much was enough to know that the problem was with the day light saving time part of code. Some engineer hypothesized that problem might be with the NTP server but his hypothesis was wrong because NTP server was dealing in UTC.
"(2) Available tools and instrumentation that allow you to inspect a running program (I'm old enough to remember debugging by adding commands to print state to the console)" -- I dealt with code which installs the firmware, frequent power cycles made keeping a debugger attached an exercise in futility so I just continuously logged the top two frames of the stack by using a system call. Crude way to trace the control flow but helped me in understanding the installation process a lot.
"(3) sufficient experience and sophisticated understanding of the system to be able to make valid hypotheses and design tests." -- This was even more important while dealing with firmware hangs, dealing with hangs made dealing with crashes look easy. Crashes were the messy criminals leaving a lot of clues behind. Hangs are the type of criminals who would have to be caught while committing the crime.
I would also like to add one more --
"(4) When debuggers fail you, git-bisect is your only true friend." -- I once was dealing with a memory corruption bug, in a piece of memory which was shared by two systems, the number of processes with access to that piece of memory was bonkers. I decided to brute-force my way out, it worked in the last release, it stopped working this release, I just kept doing a git-bisect between clean and dirty states and found the code which caused the bug. This way was definitely not the clever way to do it, but brute-force is sometimes the only option left.