Limitation of Magick?

Hi, I am new to the forum, though I have followed you closely on YouTube. I am very new to the black arts and am trying to learn as much as I can. In one of your podcasts with Nate Bales, you stated that one of the reasons that you initially hesitated to do rituals for hire was because some people would ask you to do things that were outside the scope of reality such as keep them from prison when they slaughtered their whole family, etc. In other videos you seem to say that there is no limit to what black magick can do. There seems to be a tension between those two statements. How do I know when a goal is reasonable versus unreasonable?