Bringing up people like farmers is kinda not relevant here as, quite frankly, the people who do that sort of thing are a whole lot different than your average urban dweller, but the vast majority of the population is urban. Sure, they're heavy planners, but their lifestyle requires it. Your average person isn't going to base their life around what's growing in their backyard, so to speak. Joe Public in the big city is the type of person that calls me when their cell phone goes out claiming their life is ruined because they can't get everything done NOWNOWNOW and don't have the patience to find a way around even that simple of an inconvenience.
Teachers plan a curriculum, but even then it's a eight month thing that then gets reused with minor changes over and over again, and is often at least partly copied from other sources. That's not long term planning, really, it's still fairly short term in the overall scheme of things.
Individual people may be good at planning, but that just puts more weight on what Tai said: if it was really that common for people to plan long in advance, that story about the hairdresser cousin wouldn't be abnormal, or possibly would because the parents wouldn't object because they would expect the planning to work.
Basically, what I'm trying to get around to and not finding a good way to get to it is, if people have any way that they can get benefits in the short term that don't require the long term, they take it. They see the good things, and don't stop to think about what this means down the road. The same thing happens if they're forced to take a short term hit that will benefit them in the long run; they don't look past now. The things you're bringing up, while they aren't totally invalid, are also things that generally don't -have- the short term solution in the first place. You brought up farmers, but there is no short term solution to getting food, there has to be the farms. Teachers have to plan a curriculum, there's no other way you can teach. If you just skip ahead, the students won't understand the basics and won't be able to learn anything(not that they really do anyway these days, but that's a separate topic). Also, things like games aren't really good long term plans, and even then, there's a lot of people that start it because it sounds cool, but when they find out how much effort it takes to get that character up to 70 in WoW or whatever, suddenly decide all of a sudden that they don't want to do it anymore. Which I mention because it's not that people are planning out how they're going to get to that point, they're playing around with a vague goal of getting there, they don't know what they're getting into and haven't actually planned for it.
Hmm. I got a little long winded and I'm not sure that's entirely clear. Well, basically, I'm saying people in general, not everyone, only bothers with long term plans if there's not a short term solution, and if the short term of a long term solution is bad for them, they don't bother looking to check the whole thing. At least that's my opinion from people I know and have interacted with.