Rule of Odds – Composition
The Rule of Odds states that framing your subject with 2 surrounding objects (thus creating an odd number of 3) suggests balance and harmony visually.
We tend to prefer balance and feel comfortable with these groupings of 3.
Groups of 2 or 4 can sometimes create a sense of competition where as the odd groupings tend to balance that a bit. This is a very subjective rule, but it does create balance.