It would be catastrophic (it would be a disastrous) if humanities greatest voyage (if humanities greatest quality/the human mind) was brought low (was held down) by the minds tendency to wander when left to its own devices. (by the minds tendency to wander when left by itself).
When the human mind is left alone, it may be great but also be horrible due to it often wandering.
A good paragraph is composed of a topic sentence , relevant supporting sentences, and a closing sentence. This structure is key to keeping your paragraph focused on the main idea and creating a clear one
