The most common reason is a faulty flasher unit.
The most common reason for graft failure is the formation of a hematoma, or collection of blood in the injured tissues.
Fragments, comma splice, and run-on sentences are the three most common types of sentence errors.
Sadly, I think the most common reason for picking a political party is "Because that's what my parents were".
cheating
Obesity.
The most common reason for a doorbell breaker to malfunction is usually a faulty wiring connection or a worn-out doorbell button.
The most common reason for failure to obtain federal assistance is lack of adequate documentation.
The most common reason for a Catholic annulment is the lack of proper consent or understanding at the time of marriage, which can invalidate the sacrament in the eyes of the Church.
Pilot error.
Getting drafted.
abortion