The antonyms for the phrase "saying what one thinks" include phrases such as "keeping one's thoughts to oneself," "remaining silent," or "holding back." When someone chooses not to speak their mind, it can be due to various factors, such as fear of consequences, social norms, or lack of confidence. It can be challenging to find a balance between being honest and respectful of others' feelings, but communication is crucial for healthy relationships and personal growth. To ensure effective communication, it's crucial to choose one's words wisely, actively listen to others, and express oneself in a respectful and considerate manner.