The key is to remember that historically speaking, housing appreciates around the same rate as inflation. You can get lucky and be in the right place at the right time - but if your place doubled/tripled in value, you probably already did that. There's generally no reason to expect indefinite increases in RE prices, or that housing prices will outpace inflation in the long run.
Of course if you don't have anything better to invest in, there's no point in selling. But I see a lot of people here (which is a Bay Area/VA and DC/NYC heavy forum) who seem to think that they are geniuses because their house appreciated a bunch in the last 5-10 years, and that they're going to see continued appreciation like that going forward. I would not bet on it.
-W