Ah Beng and his four friends were on a trip when the battery failed and they could not start the car. So Ah Beng said to  his four friends. Maybe if we push the car and engage the gear, we can start the engine. So his 4 friends  pushed the whole day and were very exhausted but the taxi did not move even an inch. 
Why could Ah Beng and his friends not move the car ?
Because two Ah Bengs were pushing from the front and two from behind!