Job was a man that these friends knew quite well. Here was a man that was greatly blessed by God, respected by many, and clearly following God. These friends watched as they sat with Job for 7 days his misery and pain. Did Job's wife come out to apply ointments from time to time, I suspect that she did. Perhaps his friends helped with that as well. Anyway they knew his suffering.
Job does what many of us would do initially in time of suffering he cries out lamenting or grieving, expressing the pain. It can take a moment to focus on what is important.
How often have we done the same thing at first when suffering comes? There is some hint in his words that his friends are not comforting and perhaps some blame put on God for "hedging him in" (Job 3:23)