"The vrttis are fivefold and of two kinds: afflicted, painful and impure, imbued with kleshas (klishta); and not afflicted, not painful, pure, not imbued with kleshas, (a-klishta)." Swami Veda Bharati
Explanation: There are five types of thought waves, and these five types of thought waves are of two kinds: Those that lead to sorrow, klishta, and those that lead out of sorrow, a-klishta. Latent subtle impressions are left in the mind by all mental processes. These latent impressions are called samskaras. As boulders in the bed of a stream affect the surface of the water that flows over them. so the sanskaras affect the flow of the mind. The samskaras again give rise to mental processes like those that created the samskaras. So, samskaras created by mental processes that lead to sorrow, will give rise to new mental processes that lead to sorrow.