Once my mother told me to do something that I thought was beyond my physical ability and I said, "I CAN'T".
My parents never hit any of their four children. There was one exception. When my mother heard me say, "I Can't". She slapped me and said,
"PENNY, CAN'T IS NOT ALLOWED IN YOUR VOCABULARY!"
I had to try to explain that philosophy when I was charged with "lying" on a Government Employment Questionnaire when I marked the 'Are You Handicapped' box with an emphatic "NO"