I've a beginner at practicing. I did very much so up until doing the responsible adult life thing - getting married, having kids, etc. But my wife & I are no longer together. I have concentrated very hard, tried many spells. Honestly, I make my own for I believe it's the energy you put forth more so than the ritual itself.
Without going to deep in to my situation, I can say that I have successful hindered my ex-mil's ability to continue to do more damage by affecting her money. She was also in a car accident (though i did not wish harm) and she is okay, but her car isn't. Why can I do all these things, but I can't make white magic love spells work?
Is it just me? Or is it just easier?
....however, I will add that I lack the focus due to the emotion involved to get the "good" spells achieved, thus why I've been seeking a spell-caster for assistance.
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.