Ahhhh yesssss my rouge knowlage will finally pay off!
So a few things to help you out, the key words I would look for is criminal psychology or criminology when looking for books to research. Books like “crime inequality and power” and “the criminal brain”
Draw back to the good books about this kind of stuf is that they’re pretty expensive so if you don’t wanna put in the movie doing some heavy hours of researching those key words might be all you need to get a solid reason for your boy.
Now a lot of people have already listed a lot of good reasons. To be completely honest some of the most common reasons to become a “thief” or at least to hold the title of one is pure adrenaline rush. A lot of people who break into houses and storage units are doing it sometimes simply to -see if they can- and if they do sometimes they’ll take what they think is an appropriate trophy. From most stories I hear these trophy’s are simple items that a family won’t got out of their way to hunt them down for, batteries, frozen pizzas, things that they can use but nothing that would give a house hold strong reasons to send people on a man hunt- rather then just get a mechanical lock.
One of the other really common reasons is to “stick it to the man.” This -usually- happens in a younger group of people especially those who do not have and adult funding to keep themselves afloat with (or maybe they’re the main bread winner for their family because the adults are physically incapable) basically they don’t have the ability to find high paying jobs due to inexperienced within the job market and can only get low paying fast food jobs. These jobs tend to be fair paying until you realize they might be the only people within a family who can actually get a job, then a nessaessity starts with stealing the important things, things that are easy to steal, bread from the store when in the cameras blind spot, clothing for your sister cause she’s being bullied that she only has one set of clothing at PE, Advil from the pharmacy because dads having problems walking without pain now. Sometimes this mindset continues into adulthood where instead of working to get a better job, you work to get better at theft. -because now your good at it- and you should get paid for what your good at right? Least that’s what society says...
There are plenty of reasons why someone would start but the reasons as to why they -continue- is when things can get a bit sketchy. Eventually those “reasons” fall apart and in fact they still do it because they simply are good at knowing the rules to the game, and why pay for bread when you know how to steal it? I know a guy who’s parents where relatively well off, they made a good amount of money to take care of themselves and their kids, (after several years of not being able to) even after they had jobs that could support them they still stole things from stores. The guy has no excuse for them other then “they knew how to, and so they did it.”
Hopefully this helps, “reasons” crop up a lot at young ages especially when they have to make very adult choices in life due to stressful home situations. And as they grow it turns more and more into a way of life “I’m good at it so why not? I haven’t gotten caught yet.” Is basically the only mentality some people need after a while. But again.... their is a group of people who just do it for the funnies, yolo and adrenaline rushes. Reasons are varried as to why someone starts, the reasons as to why they become a master at it and continue to do it are the parts that are a bit more complicated to explain.
Lucky it sounds like your character is young so getting into it can be very simple reasons, and he could very well still just be doing it to get a high from it. So really I think anything of the reasons can work for him ^^