Seth Godin writes:
If you're going to work…
That way, you'll have something to show for it.
The biggest waste is to do that thing you call work, but to interrupt it, compromise it, cheat it and still call it work.
In the same amount of time you can expend twice the effort and get far more in exchange.
Agreed, so why don't people work hard? Here's a non-obvious reason: working hard is risky. If you work hard and fail, you don't enjoy the self-protection that less than 100% effort affords. If you get a C on a test in school, and you didn't study much, then it's no big deal — you just didn't study enough. If you get a C on a test in school, and you studied really hard for it, then you must just be dumb.
In other words, if you work hard and fail, there's the presumption that you're innately not very talented. If you don't work hard and fail, you can credibly preserve the belief or illusion that had you only put forth 100% effort, it would have worked out.
(A hat tip on this idea is owed to some writer I can't remember, maybe Gladwell.)