I think you're referring to generalisations in the sense of cognitive distortions, but this is not the case. The saying merely calls for one to be completely dedicated to whatever task he undertakes in order to maximize his chances of success. Having doubts and starting to hatch a plan B actually takes resources (mental or emotional) from realisation of the actual task.

When you say: I'll try to ... you're actually stating your doubts about you capability to successfully do whatever task from the beginning. So you've already defined what failure is and what to do in that case. But you haven't even begin the task and the journey that comes with the realisation of it. You haven't even reach the first difficulties, the first hurdles.

I hope you know that The Sith is a fictional construct :)