Now in verse 21 he cautions fathers against a misuse of this God-given authority. The misuse he has in mind is that fathers might treat their children in such a way that their spirit is broken and they become hopelessly discouraged. In choosing the broad and general word I think Paul would have us teach that parents should avoid everything that ruins a child's confidence in God and leaves him hopeless and discouraged. This requires tremendous wisdom from fathers, because not all short term discouragements result in long term hopelessness. On the contrary, our heavenly Father clearly brings short term frustrations and discouragements into our lives precisely to put us on a new footing of faith.
Great wisdom is needed here.
I'll mention two things. First, some fathers fail to BE happy and hopeful and confident in God. Fathers, what you ARE in relation to God is far more important than any particular parenting technique you try to employ. The most important work that a father can do for the sake of his children is to be converted. We know this is true from Scripture because there we are taught to imitate our heavenly Father.