measure of a downfall:
many the reasons for failure or loss there may be, but the one often thought of, and what might be considered yet so unnecessary and yes, even avoidable, is pride, in the worst sense of the word. pride or arrogance, resulting in overconfidence and a complete sense of assurance, and of right, lead to tragic failure. pride before the fall.
it is easy to see how this develops in everyday life, not just in some ancient greek tragedy. an easy childhood and early adult life, several successes along the way, perhaps. it would build a feeling of success, things that to most would seem too risky or even dangerous, do not flash warning. and then something bad happens.
there are those that plan rigorously, no doubt, and carefully consider the risk in every situation. those that experience such pride perhaps cannot truly evaluate risk? they have never suffered setbacks that for most would make them aware of danger. it is always appropriate to question assumptions you make before deciding on anything. what if it's not true? there are always only so many possibilities. have you considered all of them?
"if only she weren't so proud of herself! she thinks she knows everything!" this describes someone who is so afflicted by pride, with a bad meaning. you can imagine such a person, proud, unsympathetic, unempathetic, self-obsessed and convinced of her own glory, unaware of hubris. and then the error that forces the situation to tragedy. when bad things happen, they are always prefaced by a bad decision, as anyone who has made mistakes is aware of, though of course, you could argue that this is overplaying personal responsibility for everything and that some bad things may be out of our control, though hopefully not. you could think that perhaps pride, in the negative sense, and insanity are linked. they are not fully aware of what is going on, so certain are they of their own infallibility.
some passages of life may be carefree and going about on auto-pilot may be fine for that period but there are also times when things come to a head and decisions must be made carefully, using the full capacity for critical thinking that you have, so as to avoid tragedy.