"一流の知性の試験とは、同時に対立する二つの考えを心に抱きながらも、なおかつ機能する能力を保持することである。"

Simplified Meaning:

Being really smart means you can think about two ideas that completely disagree with each other and still keep your cool and make decisions. For example, imagine a doctor who knows that a treatment can both help a patient but also cause serious side effects. The doctor has to consider both the good and the bad at the same time and still figure out the best way to help the patient. This skill is useful in everyday life too. For instance, if you want to move to a new city, you might feel excited about new opportunities but also scared about leaving friends and family behind. Being able to think about both feelings without getting overwhelmed helps you make a better choice. This kind of thinking makes you more adaptable and better at solving complex problems.