"Try it the other way round"

A friend of mine, who enjoyed mending things, had several sayings like this:
"If it doesn't fit, try it the other way round!" and "If all else fails, look in the handbook."
Her first comment is what is sometimes called 'lateral thinking'. In other words, we should look at a question or problem from a completely different angle.

Beautiful girl: She is facing away from you, looking to the right
Ugly old woman: She is looking towards you facing right.
Called 'The Boring Figure' and first published in 1915, drawn be W. E. Hill. 

Source: Crazy Optical Illusion