One of my most memorable early lessons during my instrument training was
with a simulator. The instructor set it up, and said that the game plan was
that I was to fly to an intersection, intercept a radial to a VOR, and hold
at the VOR. I was "flying" along holding the CDI pretty good. Whoops a
little bank, level out. Still a bank, level out. OK "seems" to be coming
back now. PAUSE (nice that these simulators have that). "OK, What's wrong
with this picture?". Ummm, spiral dive? Sneaky instructor had failed the
vacuum system. It's a lesson I won't forget.
Now, if I use a simulator, and I know that whatever I plan on doing is
going to take say "twenty" minutes, I set a "random failure" to happen
between five and "sixty" minutes. That way I don't know if it's going to
happen or not.