One of the fundamentals of painting and photography, the Rule of Thirds is a technique designed to guide artists and photographers to build drama and more generally interest in a piece. The rule states a picture should be imagined as divided into nine equal parts by two equally spaced horizontal lines and two equally spaced vertical lines, and that important compositional elements should be placed along these lines or their intersections. Elements of the composition should take care to not cross the lines, and points of interest in the work should land near where two lines intersect, known as a crash point.
Aligning a subject with these points creates more tension and interest that usualy brings to a success on the social networks.
The rule was first written down more than 200 years ago and has remained a useful piece of advice for aspiring photographers and artists ever since. The rule had become established by that point and never changed.
The rule of thirds is merely a suggestion. It does not always produce the best results, photographers should not feel the need to respecting the rule. However it does undoubtedly provide a useful strategy to become a professional photographer.