Airliners usually have a hardware clip to 'gangload' all throttles together, and the 'interface' of having two or more separate levers next to each other makes

Airliners usually have a hardware clip to 'gangload' all throttles together, and the 'interface' of having two or more separate levers next to each other makes it obvious if you missed one while moving them, or notice that the clip is flipped so the levers now work independently instead of all as one. Then again, in high stress situations even totally obvious signs like this can be missed, as evidenced by the Qantas 747 crew on the famous runway overrun in Thailand some years ago. I believe in that case, a large contributing factor was when the captain went to pull the levers back over the rear detents for reverse thrust after landing on the wet runway, he only grabbed three of the levers, and left one engine running at just over idle speed.