Because what the code does is simple enough, connects to a database, runs some queries and returns the results. I know it worked because I tested it and for that kind of code there aren't really edge cases. Even if I can't validate or catch syntax errors because I'm not yet experienced enough I can see the overall structure of the code and what it does and if it runs then there's no syntax errors.

It's like with riddles, someone asks you a riddle you think and you think and you draw a blank but if you are given the answer you can instantly validate it even if you didn't know the answer before hand, same with this.