What is besetting sin? Besetting sin is a sin a Christian can easily fall into. It sometimes come from your old habits. For example, if you loved fornicating before you repented, you may have to deal with fornicating or lust always, and guide against it... Besetting sin is part of your weakness that you will need to deal with to go above measure.
Many christians have besetting sins they fall into, and these besetting sins are sometimes so stubborn that they may deal with music ministers, pastors, tongue-talking people, worshippers etc.
To deal with besetting sin, you need God's help, constant prayers and watchfulness.