Nonchalant is a property that makes one survive under extreme pressure. However, simultaneously it can be dangerous as it can lead you to make mistakes that you will not like to make. So nonchalant means

Nonchalant means being casual, calm, and relaxed - appearing unconcerned or indifferent, especially in situations that might cause anxiety. The passage describes how this easy-going attitude helps survive pressure but can lead to mistakes due to lack of carefulness. 'Easy going' best captures this relaxed, unconcerned demeanor.