A faithful priest IS strong in self-discipline; he HAS to be to live his celibate life. He can only get that from continual prayer on his part, and on OUR part, as his parishoners.
As for dealing with problems in marriages, the priest hears more about sexual problems, as well as all other problems, than almost anyone else on the planet, except possibly marriage counselors. He can provide an unbiased 'third party' to whom couples can go, as individuals, and believe that he's not taking the side of the other party.
I'm talking about the kind of self-discipline involved in relationship which a priest does not walk in. The kind of strength a man needs to discipline his desires, yet make a woman's desires come to pass.
A priest does not walk in these kinds of dynamics day by day so doesn't have the knowledge to counsel others. This is why the catholic clergy is confused and drawing effeminate men to the priesthood. If they'd allow real men in they would be a great example to families and social justice issues would not be so much to the fore IMO.