Urvashi's curse on Arjun

Once in the Mahabharata period, Arjuna went to heaven to get a divyastra, where a nymph named Urvashi got attracted to him. 

When Urvashi told this thing to Arjun, he told Urvashi that she was married to his ancestor generations ago and so she is like his mother. Urvashi became angry on this and she told Arjun that why are you talking like an eunuch, I curse you that you become impotent and you have to be a dancer among women.

When Arjuna told this to Devraj Indra, Indra offered comfort to Arjun and said that you need not panic, curse here will serve as a boon during your exile and at the time of ignorance you drown the disguise a dancer from the eyes of the Kauravas.
And your curse will only be reduced for 1 year