I, as an engineer, am used to certainty. At least I am used to aiming for it - knowing full well that I may not achieve it in every situation. While engineering doesn't always ensure perfect predictability, it is, by definition, a science aimed at minimizing uncertainity.
But little outside of engineering works this way. You would make bets in business of the type that no designer of bridges would make. The business leader is far more ready to accept failure of his bet (albeit sourly), than a bridge designer is. And this is not only because there are lives at risk in a bridge that is designed based "on a hunch". Engineers just don't like to see their efforts fail due to silly things such as "hope", "belief" and "faith."
But what about personal relationships? How far can or should we pre-calculate actions that we take? Plan too much, and you're viewed as "scheming". Don't plan at all, and you're viewed as "flaky". This becomes especially hard in delicate personal situations where you don't know whether to take the cerebral route or the emotional, spontaneous route. And the outcomes are often unmeasurable... And hence the up and down periods of self-doubt...
