Well, you can be a good thief by being good at stealing stuff but you can’t be a good thief because when your a thief you steal stuff and stealing is bad.
But on the other hand you may be forced to steal something by an even more advanced thief so in that scenario you may not be a bad person, you just did something that is bad.
And someone may have stolen [a baseball for example] and you may go and try to ‘steal’ it back you would not be ‘stealing’ it back because they stole it from you!
But if you do steal (not using all of those scenarios) you are doing a bad(or not good) deed.
So to sum it all up then you can’t be a good thief but you can be good at stealing but stealing is bad so I don’t advise becoming a thief when you are older and need a job.