Sometimes the mind may wonder about practice itself. For example, the mind may wander off into analyzing whether an object was noted effectly, or seq… - Mahasi Sayadaw

When one cultivates strong concentration by means of tranquility or insight meditation, the mind is no longer distracted by thoughts and other hindrances. Such pure concentration, continuously focused on an object for either tranquility or insight, is considered mental purification. A mind associated with such concentration is also purified of hindrances due to the power of the concentration.

Uncertainty about what is wholesome and unwholesome is called skeptical doubt (vicikiccha). It is considered a hindrance to liberation as it hinders the arising of discriminating knowledge. A person who has doubts about the wholesomeness and unwholesomeness of phenomena is unable to abandon what is unwholesome, develop what is wholesome, and escape the cycle of suffering.

The Vammika Sutta likens skeptical doubt to a fork in the road. Say a traveler who is carrying many valuables arrives at a fork in the road; if he lingers there unable to decide which way to take, robbers may catch and possibly kill him. In the same way, a doubtful meditator who falls prey to wavering and procrastination cannot continue on with practice. He or she will then become a victim of mental defilements and be unable to escape the cycle of suffering. Only when he or she abandons doubt by noting it and uninterruptedly continues the practice can he or she be liberated from the cycle of suffering.