Actually, Jesus did not tell the woman at the well to 'Go, and sin no more.'
He did, however, tell the woman caught in adultery to 'Go, and sin no more.'
Jesus also told the man who had had an infirmity for 38 years to 'sin no more, lest a worse thing come upon thee.'
Why would Jesus tell someone to do something that was impossible to do? The answer, He wouldn't.
It is only possible to 'sin no more,' when one turns to Christ when one is tempted.
1 Corinthians 10:13 declares that one does not have to give in to temptation, there is a way of escape. That way of escape is to turn to and to trust in Christ to give one strength to overcome that temptation.
Greater is He that is within you, than he that is in the world.