There we are, going along, living life and then one day we wake up with a huge boner and a loud, insistent voice suddenly nagging at the back of our mind: "Hey, buddy! Here I am! And I'm going to control your thought patterns 99.9% of the time for at least the next 8 to 10 years. Touch me, play with me."
And our lives are never the same. The hard-on seems perpetual. No matter what we do, no matter what we try to force our brains to think about, within mere seconds it's focused on the log of wood that twitches and throbs, itching for yet another release, demanding our attention.
And while it may settle down a bit once we're a little older and the concerns of living become our focus, our cocks are still down there looking for attention, rising up at inopportune moments: in the middle of a staff meeting, walking through a store, showering at the gym, driving down the street. And so it is for the rest of our lives (if we're lucky).
It's perfectly normal, perfectly natural. It's the nature of the beast in our pants.