It depends. What kind of offer are you selling?
Generally the learning curve is massive, long, stressful and expensive. I lost tens of thousands of dollars before I could consistently make ads which were profitable.
It's not like learning coding. Imagine if every time you saw a stack trace, $250 was deducted from your bank account. Learning media buying is kind of like that.
Another path is to get hired by an ad agency. They will train you and give you a budget to manage; if you lose that budget, the worst that can happen is they'll fire you (rather than losing all your stuff).
But that would be a switch in career path, which I do not think you are asking about.