A person who can't think for themselves and relies heavily on others to make decisions or form opinions is often described as being "dependent," "indecisive," or "influenced." They might be highly susceptible to external influences and may struggle to form their own judgments independently.
In some cases, such a person might be referred to as a "follower" because they tend to go along with the beliefs and actions of others without critically evaluating them. It's essential to recognize that people can display varying degrees of independent thinking depending on the situation and context. Encouraging critical thinking and self-reflection can help individuals become more independent and make informed choices.