Say for example, for years, you've been working towards a specific goal and you've sacrificed and endured much to achieve that goal. Suppose though you come to the realization that while you plan to complete the major task that will lead you to that goal, you don't want that goal anymore, you want something else. Now the tasks you've completed are not lost, they're not irrelevant, quite the contrary. The tasks have helped make you a stronger, smarter, better person.
When you're twenty years old, changing your mind about what you want out of life is acceptable but when you're forty, not so much, at least not to you, because you've been under the impression most of your life that older = wiser, at last in most cases, and changing your mind midstream throws a big goddamn wrench in the works and causes a hellacious amount of upheaval in your life. Your family and friends (unless they're just like you and get you) wonder what the hell you're doing.
I won't say you that your long-term life goal changes overnight. You don't just wake up thinking, "Oh My God. I don't wanna really be a pole dancer, I wanna help underprivileged kids in the Sultanate of Oman". No, it's more like the frog in hot water (I've hated the oft-used analogy since I was two days old, mostly because it pisses me off that it's actually spot-on and we've all been that frog at one time or another), where we're working towards a goal and doing what we think we should be doing to get there, and throughout the years we think about it a lot, which means it's simmering in our brains, and finally when the water boils, that's the point where we say "Oh hell no!". Hmm...looking back on this, it makes no sense at all because a frog in water has no idea what's going on until he's well...well beyond cooked, of course by that time it's dead so...
On second thought, the frog in water analogy sucks. The frog has no idea what's going on, but you do. So let's forget everything I just said. What's really happening here? In a nutshell, our experiences shape who we are. The older we get the more we learn, at least it's supposed to work that way. For the majority of us it does. With our experiences, we learn more about ourselves and the people and world around us. We become better equipped to make rational, grounded decisions, even if those decisions seem ludicrous to others and yes even if they throw the goddamn wrench in the works. So, really, maybe society has it all wrong. Maybe the twenty-year olds who change their minds every five minutes are the real idiots because they aren't basing their major life decisions on anything solid. Maybe we are the cool ones.
There was a time it was hip to be young and not cool to be old. Folks, I think the tables may have finally turned. :)