I have been thinking about ways to improve decision-making for a while now. Today I suddenly realized the following.
It is really important to separate the "first-order" effects/elements from the "second-order". Since all decisions are marginal (make small improvements, if at all :) , therefore the question is not really what decision can significantly change a situation (or life), but that among many small decisions/options that each can improve/affect life marginally, which ones have a first order impact. Basically, second-order effects are negligible compared to first-order effects.
If you think this separation is trivial, you are like me only a few weeks ago :) This separation is what makes a good scientific theory good! In one sense, all science is about distinguishing the first order effects!!!