A person who can't think for themselves is often referred to as "dependent," "indecisive," "follower," "sheep," or "unassertive." They may rely heavily on others' opinions, ideas, or decisions and struggle to form their own independent thoughts or judgments. However, it is essential to remember that people's ability to think for themselves can vary based on circumstances, experiences, and personal traits. Using such terms should be done with sensitivity and understanding.