Warcraft 3 "Under the Burning Sky" mission
You had to protect one character for a 30 minute period. There are 3 seperare enemy bases attacking you constantly but at the very end they all come at you with everything they got at the same time. I played this mission so many times and does in the last 30 seconds every time. Quite a few times with less than 10 seconds to go.
One of the few campaigns I've never finished cause it was too hard.
The timing is the main thing cause it's not so bad at first but the last few minutes are

Then you die and realized you just wasted another 30 minutes trying to beat this stupid mission