Momentary concentration that focuses on mental or physical objects from moment to moment is called nondistraction (avikkhepa), a mental state that is… - Mahasi Sayadaw

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.

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.

The insight process flows smoothly if sensual desires do not arise. If they do arise, however, they obstruct the flow of insight. They appear as rivals to insight, as if saying, "It is our turn; stay away insight!"