Thomas Edison said,

"Our greatest weakness lies in giving up. The most certain way to succeed is always to try just one more time."

It's okay to fail to quit as long as you keep trying to quit one more time than you fail.

Some people are so afraid of failing it paralyzes them so they never try anything unless they are sure they can succeed. People who are like that lack courage because they never risk losing and that in itself is a failure.

So be courageous don't be afraid to fail as Winston Churchill remarked,

"Success consists of going from failure to failure without loss of enthusiasm."

So failing to quit smoking is fine as long as you don't stop trying.