Why do you need a new year?

It is a strange tradition to me, to pick a random date on the calender and decide that that day will be the beginning of a new start.  Sure, it is easy to remember the new year.  It is a good particular time, a good way to gauge your progress.  But there is also a feeling of getting a "clean slate" and I feel like that is awfully odd.  If a new year can give you a clean slate, so can any new day.  People who recover from drug addiction often have this mentality.  "I have been sober since _____."  To them, that is their new year, their new slate.  This is true for everyone.  Everyone can pick any day, any moment, to be the beginning of their new slate on any issue.