Three's such a nice number. (Note today's date!) Would we still be reading a story about the two Billy Goats Gruff? The two little pigs? Imagine being granted only two wishes! Three is a number that just rocks.
I have found that when I introduce a minor motif or plot point, it serves the story best if I tap on it (at least) three times. For example, in the forthcoming sequel to Hattie Big Sky, feathers play a minor role. So, as I revised the manuscript, I made sure Hattie found a feather or feathers on three different occasions in the story. For me, those three taps give the readers a sense of a motif's significance.
And if I've done a really good job, I've left room for those same wonderful readers to ascertain the meaning of that motif for themselves.