Bèi (被) construction encompasses a strong sense of passiveness and involuntariness. When a non-human object is the subject of Bèi (被) construction, it means that the subject is in an undesirable state.
車被偷了
chē bèi tōu liǎo
The car is stolen.
When the subject of Bèi (被) construction is a human, it means that the subject is involuntarily affected by the action.
他被欺負了
tā bèi qī fù liǎo
He was bullied.
On the other hand, the passive construction without Bèi (被) focuses on the topic and the resultative state of the topic as a result of the action. As a result, a weaker sense of responsibility of the doer is shown in topic-comment construction.
蘋果吃了。
Pingguo chi le
The apple was eaten.
