The quadrennial iPhone SEs break from the annual upgrade cycle, arriving 2.5 years after their lookalikes as final versions of popular form factors (John Gruber/Daring Fireball)

John Gruber / Daring Fireball:
The quadrennial iPhone SEs break from the annual upgrade cycle, arriving 2.5 years after their lookalikes as final versions of popular form factors  —  The answer: Leap years, the summer Olympics, U.S. presidential elections.  —  The question: What are things that occur every fourth year?