learn the hard way
learn (something) the hard way
To learn or discover something through personal experience, especially that which is difficult, painful, or unpleasant. Starting your own business is really tough. I had to learn that the hard way. Everyone will tell you that becoming a parent is challenging, but you never really know what that means until you learn about it the hard way.
learn (something) the hard wayand find (something) out the hard way
to learn something by experience, especially by an unpleasant experience. (As opposed to learning in school, from reading, etc.) She learned how to make investments the hard way. I wish I didn't have to learn things the hard way. I found out the hard way that it's difficult to work and go to school at the same time.