His ma and pa always taught him to be polite. Don't chew with your mouth open, no elbows on the table, cover your mouth when you cough, hold the door open for others, yes sir, no ma'am, please, thank you, you're welcome.
When his hearing became more sensitive, his mother told him to suppress the urge to listen in on every conversation that mentioned his name: "Eavesdropping isn't very gentlemanly, young man." And when his eyes developed the ability to see through solid objects, his father took him aside and said, "Now, son, I know the girls' locker room looks inviting, but you have to respect their privacy."
In college, he taught himself to keep his ear trained only to emergencies – sirens, calls for help, screams, gun shots. He only dared to use his X-ray vision when it was absolutely necessary – to look for broken bones, sealed files, hidden entryways. Never for selfish reasons. Never for personal gain.
He doesn't give it a second thought until he finds out about Jason. That night, he flies into space, as he often does when he needs to think. From here, about halfway between Earth and the moon, he can hear, if he wants, his mother humming to herself in the kitchen in Smallville. He can see into his desk in the Daily Planet bullpen, from which Lois has stolen two pencils and a stapler. He can hear ice melting in the Fortress and a gospel choir rehearsing in Chicago. He can see candles being lit in a Parisian restaurant and children playing on the Gold Coast of Australia.
And so he can't help but wonder why he refused to let himself hear and see what was right in front of him on that last night on Earth, only three weeks after, with a single kiss, he gave up Lois forever. He had dropped Lois off on the roof of the Planet, and he was trying to look at her, to remember her, to say goodbye without letting her know. As he took her in, there was no reason he shouldn't have been able to see the tiny speck growing in her belly and hear the second, faint heartbeat emanating from her.
He was getting ready to fly the untold light years to Krypton to find his family, when the closest family he would ever have was growing inside the woman in his arms.
If he had known, he never would have left.
So as he floats above Earth, he opens his ears, politeness be damned. Though he blocks out the ice melting and children playing – the sobbing and fighting and praying of those he can't help – he resolves to always listen, always watch, even if it is for personal gain. Even if it is to just know that some people are always there, always all right.
He tunes his hearing, once and for all, on three heartbeats: his mother's, Lois', and the faint, slightly irregular flub-dub of his son.