Oh, you become a father. It means a legal obligation to provide for the child you just brought to this world.
After having it, you remember a lot of stuff that you have probably forgotten. As they grow, images, sounds, and images come to your mind from a distant past when you were more or less that age.
Consequences are evident in your body as you stop sleeping, sometimes altogether to anticipate the future, change diapers or soothe a scared child. You develop a new set of skills that let you perform tasks that you probably hadn't dreamed of.
Money becomes a real concern and talking to your partner about the little ones can become troublesome due to the deep love you both feel about them.
Little by little, if you want of course, you turn into a 2.0 version of your parents, with new improved Internet capabilities and heuristic system to detect lies.
Having a child also makes you more sensitive to other children's suffering. You develop a sort of love for all the children in the world sometimes.
All in all, you learn to change and adapt because your little one(s) will make your days change light-speed fast.