Teaching is stable, but doctors and lawyers only have stability through their credentials. Clinics fail; firms contract; hospitals eliminate positions. I don't know about the past, but these days law firms are quick to expand to take advantage of new demand and new markets. Surely sometimes they make mistakes. Microsoft and Google seem stable now, but who can predict the future? Plenty of "stable" companies have laid people off, closed research labs, and sold unprofitable pieces to new owners that had no intention of keeping them running.