The great scientific experiments are done by keeping every other variable constant, and only varying the concern variable. The human race has made progress since the advent of scientific method, and we certainly owe a lot to the scientific method of discovery.
However, in much of our daily lives, we cannot apply the scientific method. Things are in constant flux, and one does not know with conviction which causes lead to which outcomes. We make reasonable assumptions based on our previous experience and intuition, and act on it.
When pressed in a corner and asked to place a bet on one of multiple futures, it bodes well to remember that whichever choice we make is ultimately only a hunch. And that, sometimes, what appears to be the right choice can yield the wrong results, or vice versa.
Improving our process can help us to reduce the chance of an adverse outcome, and that is why practice is worth it. It allows us to learn and function in a world were all else is not equal.