Precisely. Rational? It's a multivariate problem. Get married, buy a house, have kids. Now you're juggling daycare and school schedules and dependent benefits. At the same time, you have to balance developing enough technical expertise to increase your value, learning new tech to say current (while likely having less time for learning), and paying close attention to your work projects to be sure you can reduce your accomplishments to a cold, hard ROI so the angel of death passes by when the economy slows and the RIF times come.

And while more junior engineers can be forgiven 3 jobs in 5 years as they ratchet themselves up, seniors need to demonstrate they can stay somewhere for long enough to amortize their hiring, while avoiding getting stuck in a rut.

Good luck!