Once you do that first deep dive (as part of your 5 specialty dives) and realize you can perform at that depth - you get a massive boost in confidence.
... that is not necessarily a good thing ...
One of my biggest issues with taking AOW too soon after OW is the deep dive. Most divers haven't yet developed their basic skills to the point where they should go deep, regardless of how much supervision they have, precisely because of what you just said. It gives them the impression that they're somehow qualified to be there, and in many cases they're not ... not even after they've completed this dive for the AOW class. But they're then given a card that tells them they are. And because doing deeper dives is probably the most popular reason why people sign up for AOW, it sets the stage for some significant failures that sometimes end in tragedy.
Here's the set-up ... most new divers tend to use their air rather quickly. There are any number of reasons for this ... both physical and mental ... but the fact remains that most new divers have far higher air consumption rates than they will have once they've gotten 20 to 50 dives behind them. Now factor in that the deeper you go the more quickly you'll drain your tank due to pressure increases. Add to that the anxiety induced by narcosis, task-loading that can be caused by deeper diving (depending on conditions, this could be due to limited visibility) and what that does to exacerbate your consumption rate. And then factor in that most new divers don't own their own tanks, and are using rental tanks ... almost always AL80's (aka "oversized beer cans") ... and you're setting the stage for an OOA or LOA event ... particularly because most AOW students don't receive any air management techniques other than "keep an eye on your gauge and end the dive with 500 psi" without much training on how to actually do that.
Yes, the majority will manage to continue doing deeper dives without incident ... and that's a testament to how "failsafe" basic diving actually is. But we all too often read about people running out of air ... or more frequently low on air ... at depth. Deeper dives only exacerbate the problem, and getting "a massive boost in confidence" often serves to give people the impression that they're more qualified to manage a deep dive than they actually turn out to be.
I think if people are going to be encouraged to take AOW straight from OW, then they should drop the deep dive from the program and offer it at a later stage in the training progression ... allowing students to get more comfortable with their skills, and reducing the task-loading of managing a dive before going deep. Or, if deep diving is going to be part of the program, mandate that there are some dives between OW and AOW to allow the student to get more acclimated with their skills before signing up for the class. More emphasis on gas management, dive planning and good buddy skills should be incorporated into the AOW program to better prepare the diver for deep diving. And possibly add a section and a dive into the program that teaches the diver how to deal with task-loading before going deep. These would reduce some of the accidents we see that are caused by people going deep before they're ready for that sort of dive ... and it would enhance the overall experience of the class.
Confidence can be a great thing ... but it can also be a bad thing if it gives you the impression that you can handle dives that are beyond your ability. And you don't want to discover your real limitations in the middle of a diving incident ... that path generally leads to a less than fun experience for all involved, even if it ultimately turns out OK.
... Bob (Grateful Diver)
