Christmas comes but once a year.

Christmas is an annual occasion, and the saying treats that rarity as a reason to enjoy its pleasures while they are available.

It can also justify a modest departure from ordinary restraint: an occasional celebration may warrant a treat that would seem excessive on an ordinary day.

Use it to encourage someone to enjoy a Christmas treat or to explain a small indulgence of your own. It can sound warm and playful, especially when everyone recognizes that the occasion is an exception to an everyday habit.