Does it start when a left-handed child is forced to write with its right hand?
This was a compelling theory in the 1920s from the United States. It lasted for decades and some children went through periods with one hand tied behind their backs in an attempt to 'undo the damage'. Eventually the theory was properly tested and there was no evidence to support it. Lots of children had been made to use their right hands without 'knock-on' effects at all. Left-handedness does not seem to be relevant.
Can you catch it?