Inconsistencies with box collider walls?

I am new to Unity and the C sharp coding, and have starting watching the Unity tutorial on making a ball rolling game. I followed the tutorial but instead of duplicating the first box collider wall and rotating it, i instead re-scaled it to the desired location. However, I noticed that depending upon how the wall is rotated, it will either work or not work with the player sphere. My question is why does the wall work some times but not others, and avoid guessing each time? Thanks in advance.