To err or not to err

One of the things that has been taxing me as I have been twiddling thumbs in airport lounges recently is, that given that a single decision may prompt numerous consequences, some good some bad and others neutral, how do you make a definitive choice as to whether or not major life decisions (i.e. those that involve high levels of emotional input), were well made or not e.g. emmigrating, getting married, the decision to have children etc? I don’t think a simple weighting system is sufficient (what exactly was John Mill’s unit of utility that I studied all those years ago?..http://en.wikipedia.org/wiki/John_Stuart_Mill) especially when at least some of the consequences may not be immediately obvious. Hmmmm…