Om Swami
What is self-control and why does a wandering mind make it impossible?
Self-control means a focused mind
Self-control, or sanyam, means keeping the mind focused, and while the mind wanders, restraint is not possible. Without restraint there is no yoga (union), and without yoga nothing is attained.
One whose mind becomes focused has self-restraint, because as long as the mind wanders, restraint is not possible, and without restraint there can be no union.