Tradition is a strange animal; where does it begin? Often from fear or necessity, rituals devised for protection or to give the illusion of safety. Something done or said by chance protects the fearful, so they decide that’s the key to their safety.
Every culture in the universe has its own traditions. Earth has Morris Dancers, shaking hands, and saying ‘Bless you’ when someone sneezes. The Qualf shut their eyes and turn in a circle when the sun goes down, to ensure it will rise again in the morning. It always works.
The Doctor traditionally has companions. That works too.