YouTube: https://youtu.be/1WjqFkkgK68
The sin leaves a trace in the heart of the doer as was narrated in the books of hadith. The Prophet, peace be upon him, told us that when a believer commits a sin, then this sin would leave a black dot on his heart. If one repents from that sin then his heart would be cleansed from it, however, if one commits more sins, then this black dot would expand until it covers all his heart.