To have a grievance is to have a purpose in life. — Eric Hoffer
You are slow to complain. This is because you only complain when you are very sure that you have a significant, valid grievance and that pursuing it stands a reasonable chance of changing things for the better, from your perspective. You seldom complain just to express displeasure, resentment, or dissatisfaction. You complain because you want to change something and think you will succeed. Complaints are, thus, proactive, not reactive.