How Research Projects End

Research projects only ever end for one or both of two reasons: (1) you run out of time, and/or (2) you get bored and move on.

They're never truly finished in their entirety, and anybody who tells you otherwise is full of crap.

Update: Jaideep Singh points out that "run out of funding" is a third distinct possibility. (However, as I am a mathematician and thus have very little funding anyway, I am generally able to avoid the third option entirely.)