When something has been said, a team of four horses cannot overtake it.

When something has been said, a team of four horses cannot overtake it. (Horses cannot chase back the words you have said).  — One of the meanings of this proverb could be… Once you have make a promise or say something, you cannot take it back. People have to be responsible for what they say. Only speak after careful thought; do not speak without thinking of the consequences. Looking back, a four horse-drawn wagon was the fastest land transportation at ancient time (This is a rough translation from a Chinese proverb)