I was thinking about the three-year rule while reading about Malcolm Gladwell’s observation that it takes 10,000 hours to become truly expert at something. If you really throw yourself into a job, you’ll spend 60 hours a week working. That’s 3,000 hours a year (allowing for vacation), which means you’ll hit the 10,000 hour mark a few months after your third year. So maybe that’s where the three-year rule comes from. You’re now expert at what you set out to master. Great. Now go do something else.