Why should you feel disappointed in your child, if this is you who failed to raise him? Feel disappointed in yourself. Because you have failed to make him understand that stealing is bad.
So if you tell your child that it’s bad to steal, does that mean they won’t steal? Even if you tell your child something's bad and they shouldn’t do it, don’t be surprised that they will go behind your back and end up doing things that you warned them not to do. If things like this happen, are you going to blame yourself for that? I'm sure most parents do tell their children that stealing is bad, but some children won’t just listen.
It’s is your fault that he has used gambling to get more money for example, or did not know when to stop. You should have explained all that, but the kid only did what he thought was right. That is the problem of many parents, instead of searching the root of a problem, they blame only the final link.
Some parents don’t even know that their children are gambling, gambling can be done even with mobile phones now, so children secretly gamble with their phones that even their parents won’t know they are gambling, and you don’t expect parents to monitor even their children’s mobile devices. At least they also have privacy, which should be respected, so if children are gambling, the blame shouldn’t be on parents alone.