Kids have to change grades every year. You hit 18 and the system says it's time to move out and go to a whole new place. Four years later, another cycle…
How often do we say, "three months from today, I will be doing something totally different than I'm doing now?" How often do we look at an asset (an organization, a source of income, a technology) and acknowledge that it's our past, not our future?
A generation ago, you might be able to go forty years without being forced into a leap like this. In many industries, though, it might even be forty weeks (or forty days).
Not something to be avoided. Something to initiate.
People don't like changing their rhythm. If you adopt the rhythm of stability, then change is a threat. Adopt the rhythm of change, though, and you'll get restless right on schedule.