Why do children enjoy the rides in amusement parks, knowing that they will be scared, even sick? Why do explorers endure suffering and pain — knowing that their very purpose will disperse once they arrive? And what makes ordinary people work for years at jobs they hate, so that someday they will be able to — some seem to have forgotten what?
There is more to motivation than immediate reward. When we succeed at anything, a lot goes on inside the mind. For example, we may be filled with feelings of accomplishment and pride, and feel impelled to show others what we've done and how. However, it is the fate of more ambitious intellects that the sweetness of success will swiftly fade as other problems come to mind. That's good because most problems do not stand alone but are only smaller parts of larger problems. Usually, after we solve a problem, our agencies return to some other, higher-level cause for discontent, only to lose themselves again in other subproblems. Nothing would get done if we succumbed to satisfaction.
But what if a situation gets completely out of our control — and offers no conceivable escape from suffering? Then all we can do is try to construct some inner plan for tolerating it. One trick is to try to change our momentary goal — as when we say, It's getting there that's all the fun. Another way is looking forward to some benefit to future Self: I certainly shall learn from this. When that doesn't work, we can still resort to even more unselfish schemes: Perhaps others may learn from my mistake.
These kinds of complications make it impossible to invent good definitions for ordinary words like pleasure and happiness. No small set of terms could suffice to express the many sorts of goals and wants that, in our minds, compete in different agencies and on different scales of time. It is no wonder that those popular theories about reward and punishment have never actually led to explaining higher forms of human learning — however well they've served for training animals. For in the early stages of acquiring any really new skill, a person must adopt at least a partly antipleasure attitude: Good, this is a chance to experience awkwardness and to discover new kinds of mistakes! It is the same for doing mathematics, climbing freezing mountain peaks, or playing pipe organs with one's feet: some parts of the mind find it horrible, while other parts enjoy forcing those first parts to work for them. We seem to have no names for processes like these, though they must be among our most important ways to grow.
None of this is to say that we can discard the concepts of pleasure and liking as we use them in everyday life. But we have to understand their roles in our psychology; they represent the end effects of complex ways to simplify.