It's rare, but it's happened before - twice that I know of. Scenario is the pilot misses one outboard thrust lever, then in the process of lifting the reverse piggyback levers somehow nudges the remaining thrust lever forward. Both cases that I'm aware of happened interestingly in Korea - the first a passenger 747 at the old Seoul airport (Gimpo), I'm thinking in the 1990s, the second a freighter 747 at the new Incheon about 10 years ago. In both cases the aircraft went off the side and did a half spin in the grass. No serious injuries. Memory says the first one was Korean Airlines, the second a middle east freight outfit.