There are three kinds of complaints we may make in times of distress. The first is natural and spontaneous, as when the body groans and complains, weeps and laments. There is no fault in this, provided, as I have said, that the heart is resigned to the will of God. The second kind of complaint is that of the mind, as when we make known our ills to someone who can give us some relief, such as a doctor or a superior. There may be some imperfection in this if we are too eager to tell our troubles, but there is no sin in it. The third kind is sinful: that is when we criticise our neighbour either to get rid of an evil which afflicts us or to take revenge on him; or when we willfully complain of what we suffer with impatience and murmuring.
--St. Louis de Montfort, Letter to the Friends of the Cross