If you hire your neighbor for $100 to dig a hole in your backyard and then fill it up, and he hires you to do the same in his yard, the government statisticians report that things are improving. The economy has created two jobs, and the G.D.P. rises by $200. But it is unlikely that, having wasted all that time digging and filling, either of you is better off.
People don't usually spend their money buying things they don't want or need, so for private transactions, this kind of inefficient spending is not much of a problem. But the same cannot always be said of the government. If the stimulus package takes the form of bridges to nowhere, a result could be economic expansion as measured by standard statistics but little increase in economic well-being.
And of course we all remember the first rule of holes -- if you're in one, stop digging.