Overestimation is the cause of suicides but at times, also of success. Contemplation is a good habit that saves us from many troubles but overthinking ruins it all. It harms our self-image and self-confidence. It prevents us from working hard to achieve our goals by making us afraid or lazy.
When we contemplate, we evaluate both the positive and negative facets of a situation whereas when we overthink, our mind is colored with solely the negative consequence. Contemplation might open to us the ways to achieve our desired object but overthinking increases unnecessary worry at each step and by focusing on the negative consequence, closes all the ways that can be followed and stops all the work altogether.
Both are the activities created by our brain but overthinking is the cause of stress whereas contemplation prevents us from getting to a point where we might get stuck and the stress that will be generated from it. Overthinking ruins everything, be it projects, relationships or our self-confidence and contemplation saves any mishap from occuring. Both are two facets of the same activity—thinking but overthinking ends life whereas contemplation saves it.