It seemed like a Good Idea at the time
Words to live by. To know and cherish. To explain away whatever horrendous monstrosity you have created by doing precicely what no sane person would do at gun-point. Truly a wonderous statement, to be used at every possible circumstance.
The people who use this statement are not, or at least weren't, at the time, sane. Only a certain number of activities warrant this title; fact of the matter being that anything ever done must have seemed like a moderately good idea to someone at the time, or at least better than the alternatives, and so it was done. Examples would be paying bills, or going to the movies. But to be worthy of the moniker "it seemed like a good idea at the time," there must be some indication that it probably wasn't a good idea for any reason, even if it's your good sense returning and saying "my word, do you have any idea how fantastically stupid that was?" to which the only reply is, indeed, a sheepish "it seemed like a good idea at the time." Good sense returning and informing you of such idiocy is, of course, better than being informed by your parents, spouse, S.O., neighbors, boss, professors, the police force, or, in the most extreme cases, the angry mob.
The pinacle of this statement is not, of course, in the mere application of it after the fact. That is but Ramen in the vast world of pasta. No, the true pinacle comes from realizing before any event occurs that "it seemed like a good idea at the time" will be the perfect description, later on, of what you are planning. It is epitomized by dialogues that sound something like this:
Tom: "Why are we putting M-80s in the microwave, Jim?"
Jim: "You know, now that you mention it... I haven't got any idea either. To see what happens, I suppose."
Tom: "Isn't it likely that they'll just explode?"
Jim: "Well, yes, but you'll notice the pile of sandbags over there."
Tom: "Ah, good thinking. ... Dang, this is going to be so very cool."
Jim: "Oh yes. ... Are you sure this is a good idea?"
This unwitting pair is about to recklessly endanger their lives for rather silly reasons. They have reached the epitome of the "it seemed like a good idea at the time" philosophy. Study their words, make them your own, and your life will suddenly become far more interesting.
Not necessarily shorter, but that's also a good possibility.