Nirlep means non stick. In Bhakthi, Sadhus thought nothing sticks in the Athma meaning Nirlep. They think it is the body that enjoys happiness and sorrow, so the Athma just comes in to the body and acts.
But Paramathma says Athma has 3 Faculties namely Mind, Intellect and sanskar. It is in Sanskar all our actions or karma is recorded, the good ones gives us punniya and the bad ones gives us Pavam.
So telling Nirlep or non stick about an Athma is wrong.
Like wise when we realize that we are an Athma and then perform our act we can view this life as a witness, there by what ever we see will not hurt us. This is also a kind of nirlep or non stick which means Athma is not disturbed by the external acts.