Originally Posted by 757FO

And yet everyone complains when we keep the seatbelt sign on, and think it's some grand conspiracy to avoid serving the paxs.

Originally Posted by narvik

Likely a matter of 'for how long' though: almost everyone understands seat-belts being on for when turbulence is about to be expected or is actually occurring. Reports/'complaints' made on here are often because of the seat-belt sign being on for extended periods where it's deemed unnecessary.

Furthermore, it's a bit unclear whether the seat-belt sign was even on in this particular story here, but it appears it wasn't.
So, unless the seat-belt sign stays on for the duration of the whole flight, unexpected turbulence will just occasionally happen even with the seat-belt sign turned off.

(I keep my seat-belt on for the whole flight unless I happen to get up -which is rare-, so having the seat-belt sign on doesn't really bother me personally.)