A file in my template finding the path of a file 5 directories up w/o mapping

I’m so confused. A few days ago, I had the errors that let me know that I was calling a file that wasn’t in the directory, because I was trying to include the file db.php without the path to the actual file that was a few directories above the template folder. Now, after a few edits, I am able to include that page without defining the path-just by including db.php. It’s like this with other files, too. Why is this happening?