The parent who is not consistent in his conduct cannot truly exercise discipline in the case of the child. A parent who does one thing today, and the contrary thing tomorrow, is not capable of sound discipline. There must be consistency, not only in the reaction but also in the conduct and the behaviour of the parent; there must be pattern about the life of the parent, for the child is always observing and watching. But if he observes that the parent is erratic and himself does the very thing that he forbids the child to do, again you cannot expect the child to benefit from any discipline administered by such a parent. There must be nothing erratic, capricious, uncertain or changeable in the parents if they are to exercise discipline.
Another most important principles is that the parents must never be unreasonable or unwilling to hear the child’s case. There is nothing that so annoys the one who is being disciplined as the feeling that the whole procedure is utterly unreasonable. In other words, it is a thoroughly bad parent who will not take any circumstances into consideration at all, or who will not listen to any conceivable explanation.
D. Martyn Lloyd-Jones, Life in the Spirit in Marriage, Home & Work: An Exposition of Ephesians 5:18-6:9, pg. 280