The difference between a good haircut and a bad haircut is three days. My long-time barber explained his philosophy noting that three days is the time that it takes to get adjusted to something. While I would make an exception for a horrible or really uneven haircut, I agree with his general sentiment that we get accustomed to new things very quickly.
Our ability as humans to quickly adapt to new situations is a wonderful skill, but I wonder how much we lose in the adjustment. This is especially pertinent in the religious life of a monk, cloistered nun, or even a friar where we come together to pray four or five (or more) times each day in the same chapel, chanting the same sets of psalms, week after week. This routine has its dangers as it is so easy to sing on auto-pilot and not pay attention to what we are doing or saying.