Use ～がち to say something tends to happen or that someone is prone to doing something — almost always with an undesirable or unintended tendency (oversights, delays, misunderstandings). It is common in analytical writing, reports and meeting commentary where you generalize about a recurring problem. Compare ～やすい (easy to / physically prone to) which is neutral, and ～ぎみ (a slight touch of a condition right now).