Bruce had always doubted himself. After growing up in a broken home, constantly shut up in his room out of fear of getting hit with a vodka bottle, you couldn't blame him. His farther would convince himself his wife Rebecca had given birth to a mutant son due to his work with radiation. Brian was driven by an insane jealousy of Bruce as he was a object of Rebecca's love. Brian was then tipped over the edge during being intoxicated and began to abuse Bruce frequently and murdered his wife. As a result of his actions Brian was shut up in a mental asylum and sentenced for life. Bruce was then sent to live with his auntie, Susan who was understanding of his rage after his childhood sufferings and raised Bruce as her own.
At 18 Bruce graduated science high school, the went on to desert state university in New Mexico with no distractions or people to hold him back. As a scientist Bruce picked things up well, cloning, robots and the supernatural field.
Bruce was obsessed with creating life wether they were robots or humans brought back from the dead. What Bruce couldn't perfect was creating human life from scratch. Failure after failure he wouldn't give up. He knew it could help. Loki's attack on New York made him cautious of security and how he and the avengers could help. Until one day he became aware of his childhood and the way he grew up. He thought to himself 'I want to care for a child of my own and show them that there is always someone there for them.'
As of his master in science he was able to try all sorts of new methods, electricity and considering organ donating. He would collect organs from different science labs to create his own child. He had no one, he wasn't in a relationship, but he wanted a child, not a girlfriend.
He would succeed.