Why can I only do dark spells?

Many years ago I was in the same situation. The most powerful spell I ever cast was designed to hurt someone, and it was very effective. At first I was excited, but later I felt a great sense of regret and remorse. Now I don't like going completely dark at all, though I do often stray into grey territory with a carrot AND stick approach "Not moving toward the desired outcome of the spell fills the target with dread, and anxiety, but doing so instills a sense of comfort, peace and satisfaction." That way you are both pushing and pulling toward the desired outcome.

Okay, I went off on a tangent. The simple answer is passion: If you can direct it is is a potent weapon to fuel your spells. If you can't is messes everything up. When you are upset, hurt, etc, you have a lot of passion and it sounds like you are able to channel and focus that into magick thus making your spells more potent. Also comparing the spells you describe, they are different classifications of magic. Dark spells typically target a specific individual. I don't have the details, but there's direct manipulation of a subject involved. With something like a money spell it's more generalized. Yes you have a specific target (The person recieving the money), but most people don't specify where that money is coming from. That's a rather large component of the process, yeah? These generalized spells work with totally different formulas which may be harder for some people to cast. I know they are for me. It also may be that you're less adept at channeling different kinds of passion into your work to make it stronger, or you simply have some kind of subconscious block telling you that you are not able to succeed in this kind of magic. Faith/Conviction are the #1 most important component of any casting and if you don't have it for whatever reason the spell won't work.