This is the number one reason. Mission 6 ("Fuel Depot") and Mission 12 ("Eagle's Nest I") are notoriously long. Spending 50 minutes silently eliminating guards only to be spotted by a random patrol in the last courtyard is soul-crushing. The trainer allows you to practice the second half of a mission without replaying the first half for the hundredth time.
# Assuming we're using Windows and the game is running in the same architecture (x86 or x64) kernel32 = ctypes.WinDLL('kernel32', use_last_error=True) igi 1 all mission unlock trainer
process_handle = kernel32.OpenProcess(0x10, False, pid) if not process_handle: return False This is the number one reason