"Things take longer in the short run but they happen faster in the long run."

The way I've heard it is that most people overestimate what they can accomplish in a day, but underestimate what they can accomplish in a week/month/year.

I've heard it phrased as "We overestimate change in the short run, and underestimate it in the long run"

http://www.boingboing.net/2008/01/03/roy-amara-forecaster.ht...

E.g. it doesn't take long to go from "OMG online Social networking"? this will change everything! To "eh, my life is still the same". Then year later, you notice how much your social life has been slowly but totally extended and rearranged.

Ray Kurzweil also likes to point this out. It's his explanation for why we don't appreciate how fast things are actually changing.