Why can't bathrooms be square

At first glance nearly every room appears to be square and the walls vertical! Having just tiled my bathroom I only wish this was the case.
Unfortunately the start wasn't as straight forward as I had hoped as a leaky shower screen over the bath had made the floor a bit dodgy, so that needed to be rectified first! 18 mm play was the answer and well screwed down, we needed to get a plumber in to disconnect the water and toilet so we could tile the entire floor.
In my infinite wisdom and to match the wall tiles, I had chosen a porcelain floor tile, they look the part, however they are pretty tough and take a lot more care to cut than a ceramic tile.
After a day of messing around the floor was finished, except for the grouting - hooray.
Then onto the walls. The plan was to half tile most of the bathroom, except around the shower that is over the bath, with a natural pebble border to go around the top of the half tiled area.
I thought I would start with a full tile by the door frame and move around the room from there, not good! I assumed, foolishly that the door frame would be straight, but when I got to the corner the problem became clear, so off they came.
I called a friend who is a more experienced diy expert so he advised me to start with a vertical line in the middle of the wall, which would most likely mean cutting both ends, but your joints would be vertical.
So this I did and it worked well, so the thing I learn from here is not to assume that rooms are built straight, square, vertical etc, to start by using a level to make sure the joints are straight




Thank you for reading