Besides the fact that Buddhists are told to think for themselves, and that Buddhism as a philosophy exists across many cultures, time periods, and with varying teachings and practices, there are some core Buddhism beliefs that might be considered representative of most Buddhists.
Buddhism teaches that beings experience an endless cycle of death and rebirth. If a person doesn't attain goals in her lifetime, she will live again. This may seem like doctrinal trivia, but without reincarnation, certain basic ideas of Buddhism make no sense.