learn the hard way

learn / find sth the hard way (to learn sth by experience, especially by an unpleasant experience) — узнать на собственной шкуре, тяжелой ценой, ценой проб и ошибок, набив много шишек

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.

Investing in real estate is tricky. I found that out the hard way.

see also
[school of hard knocks]
[go through the mill]
bitter experience
from bitter experience -- на горьком опыте, из горького опыта
If you know something from bitter experience , you know about its unpleasant aspects because you have experienced it before

......She knew from bitter experience it wasn't worth complaining. (MM)