The original reason that Bruce Wayne chose the Batman identity is not one that fans would expect. Detective Comics #235 reveals one of Batman's major secrets. It's one that has long been forgotten, but is worth knowing about.
Bruce Wayne has had numerous variations for why he selected Batman as his alter ego to fight crime. Typically the reason is that he had a fear of bats that he took over to transfer over to strike fear into his enemies. However, there is another reason and it is much more surprising - so much so that Bruce hadn't even remembered it himself initially.
Detective Comics #235 has the creative team of Bill Finger, Sheldon Moldoff, Stan Kaye, and Jack Schiff. While this issue from 1956 is known for revealing that Bruce Wayne's father, Thomas Wayne, was the first-ever Batman, it also reveals the true reason Bruce decided to dress up as a bat. Like many fans, Bruce believed that an encounter with a bat is what caused him to select the bat as his icon. That belief stemmed from Bruce spending a night contemplating what would best bring about a feeling of fear in criminals.
That same night, a bat flew in through the window with Bruce believing it was an omen - a sign that a bat was exactly what he needed. He soon realizes that this isn't the case at all. The appearance of the bat that night triggered a "subconscious memory" of the first Batsuit. Reading through a journal left by his father, Bruce discovers an entry stating that young Bruce loved the costume and wanted to wear one like it - to which his father responded by saying he would save it for his son. Now, Bruce realizes that the bat he saw was just a means of remembering his father's Batman costume - a costume that was saved just for him even if he didn't find it until after he made his own.
Even without being given the suit, Bruce was able to make good on his father's statement about him wearing one when he grew up. Since he couldn't have his father's, Bruce unknowingly created his own iteration of the suit and used it the way his father did the night the Batman was first created. What started as a simple masquerade party attended by Bruce's parents turned into a lifelong promise to protect Gotham under the dark of night in the guise of a bat. While the aspect of fear is certainly important in letting Bruce accomplish his goal, it wasn't what brought about the identity and costume to begin with.
This version of Batman's origin is one of the most nonchalant and somewhat non-dramatic versions of the story. Often Bruce is seen being surrounded by bats in a cave he explores or stumbles across, causing him to be traumatized. He then turns this trauma into a weapon to wield against others, embracing his fear. Bruce's creation of the Batman suit and all other aspects of his vigilante quest do not happen until after the death of his parents. Instead, this issue throws that idea out of the window, showing that Batman was already in existence long before that fateful night in the alleyway. Bruce likely would have worn the costume eventually, perhaps just to a single party instead of as a vigilante uniform. Now, with Infinite Frontier folding stories from all eras of DC Comics into the current continuity, this could very well be a canon origin. Regardless of which origin fans like better, one thing is true - the idea of Batman was always going to find a way to exist in Bruce Wayne's life.