The Joker, of course, has a theory:
The difference could be that wives and children can be replaced—for tax purposes, if not in our hearts—whereas birth-parents cannot, but while that's true, that's not the most significant difference. The most significant difference—the one that, despite not knowing the secret identity of the Batman, the Joker deeply understands—is that "one bad day" is far worse when, instead of being told of a death secondhand, you witness it yourself. Hence, his plan:
The Joker could have chosen to abduct Barbara Gordon off the street and dump her in the river, but instead he waited until Commissioner Gordon visited her apartment, because he knows that losing someone you love is one thing, but witnessing that person's death causes psychological trauma of a far greater intensity.* In short, without knowing that Bruce Wayne is the Batman or how he came to be the Batman, the Joker knows exactly how to make a Batman: make the victim watch.
Lest you think that either the Joker or myself are pushing this argument too far, consider the visual history of the Batman's formative moment. It was first represented in Detective Comics #33:
There's almost a duo-specific word-picture relation coursing from the first panel to the next. The text of the first declares that "[t]he boy's eyes are wide with terror and shock," and the second depicts the boy's eyes, wide with terror and shock. The focus, textually and visually, is on Wayne's eyes. On what he sees. The second, and first fully fleshed out, representation occurs in Batman #47:
How significant are the young Wayne's eyes in this panel? They've been isolated from his head and framed with anger. It's not the "one bad day" that changes Wayne into the Batman, because there was "something about young Bruce's eyes [that] made the killer retreat," and that "something" consisted of a combination of awful accusation and eidetic memory, though even that is not enough to transform the owner of those disembodied eyes into the Batman. (Many a poor soul has witness many a beloved one murdered, after all.) But there is "something" to those eyes, as here they are again in Frank Miller and David Mazzucchelli's Batman: Year One:
They have, I grant, been shoved back in his head, but they're still isolated in an extreme close-up. Miller and Mazzucchelli follow Batman #47 in having young Bruce's eyes directly address the readers' so that they might see what Joe Chill sees above. Only not. Chill's already fleeing in Year One, so the attention of those eyes is even more focused on something outside or beyond the frame, almost as if Wayne seeks communion through eye-contact with an unseen audience. "You understand why I had to become this," those eyes seem to plead. But no matter how you interpret that third panel above, it patently belongs to this tradition of believing that "what Wayne was seeing and how he was seeing it" is more important than "what happened to Wayne on his 'one bad day'" to the future development of the Batman.** While we're on the subject of his future development:
Here's the futuristic, Platonic ideal of the Batman from Warren Ellis's Planetary/Batman: Night on Earth. Note the isolated eyes in the inset panel. Doesn't take much to guess what was depicted on the previous page:
Look at that bullet in the bottom panel. Look how it hangs there—sans speed lines—between the whites of young Wayne's eyes. The presence of [Black, the crumbled figure from the first Ellis panel] suggests that this is no flashback. This bullet the child never saw—could not have seen—frozen in the middle of a locked stare. But who is Wayne staring at? I put my money on the guy in the [first Ellis panel].
It's the look that links the orphaned child to the caped crusader. Purely visually, the dark circles around young Wayne's eyes resemble the mask around those of the older, futuristic one. There seems to be a continuity to the representative mode employed when depicting this moment, so it makes sense that when Nolan re-re-re-re-boots the franchise in Batman Begins, he'll partake of it. We start mid-scene, with a close-up on the young Wayne after Joe Chill's approached:
The level of framing remains the same: this could almost be a first-person point-of-view shot from the young Wayne's perspective. There's even a hint of a low angle of framing, which makes the gun seem even slightly more menacing—as does unbalanced framing, which indicates where the bullet will be headed, and the extremely shallow depth of field. The only item in the shot that's in focus is the gun, because the foreground and the background are mere inches apart in an almost literal representation of Elizabeth Loftus's theory of "weapon focus."
Except! Loftus's theory argues that "the presence of a weapon adversely affects subsequent eyewitness recall performance such that memory for details such as the perpetrator’s facial characteristics and clothing is impaired," whereas the above demonstrated that "something" in the young Wayne's eyes allowed him to focus both on the weapon and the facial characteristics of the man wielding it. It's not a superhuman power, but neither is it a sign of the hypertrophied intellect that so many generations of writers have attributed to the Batman ... but it's more of a superpower than a sign of unparalleled brilliance. But I digress, as I was attempting to prove that Nolan belongs to the representational tradition sketched out in this post. Here's the final shot of young Wayne:
*Which, granted, calls into question why the Joker's psychological problems run as deep and wide as they do, since he was merely informed of his pregnant wife's death, but that's a whole different post entirely.
**This dynamic is even apparent in the draft of this post, which looks like this.