That you may work hard and you may be successful, but that doesn't necessarily mean that the hard work is what caused the success.

Correlation doesn't imply causality.

"If you don't do well in school, you'll end up digging ditches."

Now I look at that guy sitting up in the climate-controlled cab of that big Caterpillar making twice what I do with my fancy college degree and I seriously question my mother's wisdom.