"أعظم شر يمكن أن يصيب الإنسان هو أن يسيء التفكير في نفسه."

Simplified Meaning:

When someone starts to believe they are bad or worthless, it can be very harmful to them. This kind of negative thinking can make them lose confidence, stop trying to achieve their goals, and even affect their happiness and relationships. For example, imagine a student who fails a test and then thinks they are stupid. If they keep thinking this way, they might give up on studying or participating in class, which could result in worse grades or missed opportunities. Instead, it's important to recognize that everyone makes mistakes and that learning and improving are part of life. Believing in oneself and maintaining a positive self-image can help a person stay motivated and resilient. In short, thinking badly about oneself can be one of the most damaging things, but having a positive attitude and believing in one’s abilities can lead to a more fulfilling and successful life.