Part of the reason that students have trouble with trigonometry is that it seems so irrelevant and pointless. If those same students really wanted to design a house or construct a model bridge, however, they might very well be eager to learn trigonometry when it became clear to them that they needed to know it.
With this idea in mind, we can begin to see that the problem with school as it is currently constituted boils down to this: The order in which information is presented in school is more or less the direct opposite of the natural order in life. In life, individuals have goals, they formulate plans they believe will help achieve those goals, and then they decide what actions will advance those plans. Having determined the actions they must do, they ask themselves if they have the necessary skills and resources to carry out those actions. If they do not, they begin to acquire those skills and resources. This may in turn entail formulating new goals, plans, and actions just to get to the point where the original plans and actions can be executed.
Schools tend to reverse this natural order. Well, actually that's too kind, since in the attempt to reverse the order, schools often skip the most important part--making sure the knowledge that is covered is relevant to students' lives. Consider mathematics instruction. First we teach the skill of arithmetic, then we teach algebra, then geometry, trigonometry, and, finally, calculus. But what is all this for? No one really ever says.
How Goals Direct Learning
Where am I in the content of the book?