Why do people give up on their goals? Some would answer lack of discipline, others lack of motivation, or impatience, but whatever wording you choose, all these responses boil down to one reality -- real change, real accomplishment, often takes a lot longer than we anticipate, or like.

That new gym habit or diet goes down the drain after just a few weeks, for instance, because your jeans don't get any less snug. Or we give up on that book we're writing or new online business we're starting because as we wade into the confusing middle of the project, complications pile up, and enthusiasm wanes. (Science, it should be noted, has shown that motivation tends to dip around halfway to a goal.)

So how do you stop yourself from getting discouraged? How do convince yourself to be content with slow but steady progress? Blog Farnam Street recently offered a suggestion -- you could call it the "5 percent rule."

Self-improvement is like a lathe.

When we think of self-improvement, we should imagine a lathe, writes blogger Shane Parrish on the site. A what?

"A lathe, for the non-engineer, is a tool that molds a piece of material into some shapely form. A machinist would use a lathe to take a hunk of metal and turn it into a useable engine part, for example. The lathe takes something with potential and shapes it into something useful by slowly refining it and shaving away the excess," clarifies Parrish.

But unless you've worked in a machine shop, the image of the lathe might not do much for you. Another perhaps more compelling way to think about the way self-improvement slowly accumulates is this, according to Parrish: "If I can get 5 percent wiser and better every year, then I will be about twice as wise as I am now in less than 15 years. (Go ahead, grab your calculators.) In less than 30 years, my return will be 4x. This is how the non-gifted among us can surpass otherwise more intelligent people."

The point isn't that you need to precisely hit some 5 percent target (how could you know if you got exactly 5 percent healthier or happier, after all?), but that you should aim for this small level of improvement to help you keep your expectations sensible and your motivation up.

"The numbers don't matter so much as the concept: Small improvements add up to massive differences. Compounding works in other arenas besides money. And we want to compound worldly wisdom," he writes.

It's an intriguing suggestion: could you boost your motivation by reducing your (short-term) expectations with the 5 percent rule?