10002level,
On the 777 the auto throttles are normally left on while hand flying. You just need to ensure they are in "speed" mode. The danger is if you go from a non "speed" mode with the autopilot in and then disconnect. Now you are hand flying with the auto throttle turned on, but not operating. No drama if you know this and manually manipulate the thrust levers but this is not the normal state of affairs. If you expected the auto throttle to control your speed but it was in hold mode, and you were overwhelmed with manoeuvring the aircraft from a hot and high position, and you were new on type, and it was the end of a long haul flight.............
The holes all start to line up. Clearly an accident is not an acceptable outcome but the reasons for it are rarely as simple as "the crew stuffed up/are undertrained/incompetent ".