Star Trek: The Next Generation1987

[Rasmussen has refused to help Picard decide on the right choice to save a people from certain death]

Captain Jean-Luc Picard:
How can you be comfortable watching people die?

Rasmussen:
Erm, let me... put it to you this way: if I were to tell you that none of those people died, you'd easily conclude that you tried your solution and it succeeded. So, you'd confidently try again. No harm in that. But, what if I were to tell you they all died? What then? Obviously, you'd decide not to make the same mistake twice. Now, what if one of those people grew up...

Captain Jean-Luc Picard:
Yes, Professor, I know. What if one of those lives I save down there is a child who grows up to be the next Adolf Hitler, or Khan Singh? Every first-year philosophy student has been asked that question since the earliest wormholes were discovered.