There are a number of inherent problems when wallpapering. To start with, not all rooms and walls are completely square and true, meaning that patterns will not always match perfectly as they are stuck to each wall and corner.  Therefore, you have to do the best you can, ensuring that each wall has approximately half a centimetre overlap to the adjacent wall. When the next piece is hung, dependant on the pattern repeat, the difference in patterns will look less obvious and thus blend into each wall. This was the case in this downstairs toilet. Such techniques minimise differences and help to ensure a more unified appearance.