HE WHO HESITATES IS LOST, we’re told. (The quotation is actually a misquote from Joseph Addison’s 1712 play Cato, in which he says “The woman that deliberates is lost.”)
It doesn’t mean that you should leap precipitously into a new situation, but that hesitation produces unforeseen complications. Suppose you’re driving your car and are pulling out into traffic. You start to move forward, then stop, then decide it’s OK to pull out after all.
But your decision is based on old data: the position of the cars at the moment when you made the initial observation. By the time you’ve hesitated, stopped, then pulled out again, the oncoming traffic will be that much closer and you’ll be that much more likely to cause an accident.