I can think of at least 3 ways that people fail to make strategic, effective decisions.

1. (as the above post pointed out) it's difficult to analyze options (or even to come up with some of them), for any number of reasons: too many of them (and too little time), lack of information, unforeseeable secondary consequences, etc.. One can do one's best in the most rational fashion, but still comes out with a wrong choice. That's unfortunate, but if this is the only kind of mistakes I am making, i am not too worried. it's a matter of learning better heuristics, building better models, gathering more data... or, in the limit, admitting that there's a limit to how much human intelligence and limited time/resources can go, even if correctly applied to problems.

2. A second, more worrisome, mistake is not to even realize that one can step out of one's immediate reactions, stop whatever one's doing, and think about the rationality of it, and alternatives. This mistake differs from (1). As a hypothetical example, suppose the wannabe comedian generated a list of things he could do, and decided to watch the Garfield cartoon. His choice might be wrong, but it's a conscious, deliberate choice that he made. This is mistake of type (1).

Suppose however, the Garfield idea was the first thing that came to his mind, and after 3 months he was still at it, never stopping to question his own logic. This is mistake of type (2).

Type (2) is more worrisome, because there doesn't seem to be a reliable way that, if left alone, one can break out of it. Douglas Hofstadter (of GEB fame) invented a word "sphexishness", which I think describes this vividly. It's a wonderful label, and I use it to catch myself in the act. Hofstadter coined the word from sphex's (digger wasp) inability to break out from a fixed routine of laying eggs when disturbed by human. Hofstadter gave a spectrum of sphexish behaviors, from a stuck music record to teenagers addicted to video games to mathematicians applying the same trick for new discoveries. (Hofstadter, Metamagical Themas. "On the seeming paradox of mechanizing creativity").

A lot of the 'unstrategic' decisions people make smell of sphexishness. (decision here is a misnomer, as it's a lack of conscious decision that lead them to taking ill-effective actions.)

How do you correct mistakes of such a type? It requires self-awareness. Some kind of an interrupt to break one out of a loop. The ability to spot patterns in unexpected places. Ways to help yourself: hang out with intelligent, observant people (who would do you the favor to point it out for you; return the favor when you see others trapped in such a behavior). Try to develop a mental habit of self-watching.

3.There is yet a third way that people don't do what's best for them: unlike in (1) & (2), they know what they should do, but just can't bring themselves to doing it. Taking the aspiring comedian example again. Does he really think watching Garfield is the best thing to do? I doubt it. He might know that going to an open mike event is better learning, but it's so painful (the anxiety of first time performers, fear of failure) that he procrastinates -- and in the worst way too, by doing something that seems like progress (so he doesn't feel guilty from it), but actually is very ineffective. (The irony is that, the mind is actually doing the rational thing, but on a small scale: pain avoidance. but of course on the larger scale this is detrimental to individual survival, hence irrational.)

This is a situation where the best choice is not hard to figure out, but so difficult (often the difficulty is psychological, but difficult nonetheless) that the mind avoids it. The solutions seems to trick the mind into undertaking it. E.g. some people avoid thinking of taking on a large project (because it would be overwhelming), but work on small pieces of it until they built up momentum (in the form of confidence, or having made too much investment to turn back, or having expectations places on them...).

I suspect type (3) exist because rationality is a recently evolved phenomenon. Our psychology is still by and large that of an unconscious, reactive animal. Rationality and consciousness have to fight every step of the way against some hundreds of thousands of years (much longer if you count the time when we were fish and even before that) of evolved behaviors that were once useful and hard-wired.

Yet therein lies hope too. If we can find the right tricks, push the primitive buttons, we can get such amazing, barbaric, uncontrollable motivation and energy out of ourselves. The buttons might be designed for something else, but our intelligence can use them to achieve what we know is good for us. The image is using sex to encourage people to learn and act rationally (I have no idea how that might work). But the hope is that, consciousness triumphs over the lizard brain in us.