I argue that it is important to properly think things through. I believe that one not only needs to think things through, but that one needs to be systematic and methodical. This applies to almost anything I can think of. I fear that I all too often see people not being careful enough to properly think things through. Simple examples follow, to drive the point home.
You have an idea. It could be anything; you have an idea. It could be great, wonderful, mediocre, it doesn’t really matter. You can benefit from thinking things through, from systematically going through every aspect of the idea either to improve it or to prepare yourself for potential risks or roadblocks. The decision to tie or to untie one’s shoes is simple enough to accomplish from start to finish: One does not necessarily have to consider extreme existential risks when deciding to tie or to untie one’s shoes. Unfortunately, most "ideas", call the ideas, projects, objectives, goals, programs, what have you, are not exactly like tying or untying one’s shoes.
At the same time, one does not want to speculate and philosophize too much, what is often referred to as Analysis Paralysis. However, it remains true, I think, that at times what you think you want is not really what you want. Say you have an objective, a project, a goal. Call it X. X in this case I would simply call "something that you want". So you have stated your goal, that you want X. But is X really what you want, or is it just what you think you want? Is X really the X you think it is, or is it a Y or a Z instead?
Taking the time to carefully think things through can be such a useful tool for this sort of thing. It means that you will have examined the thing closely, with meticulous care, and should be prepared to follow through with it while being attentive to potential threats, barriers, ricks, roadblocks, etc. But if you do not systematically and methodically think things through, then you are leaving yourself vulnerable to "attack" (An attack from an adversary might be how one would frame it in terms of information security, but the same thing holds for many other domains, i.e. an "attack" a.k.a. "risk" from an "adversary" a.k.a. "Nature". It doesn’t have to be an actual attack per se, it just means a situation where you are vulnerable to disadvantages).