You’re dealing with things that are real. You need a state of desire. But you can’t be keyed up, or chasing after the vision. You can’t be overly anxious or attempting to force yourself to experience something. Sometimes you won’t see something. Sometimes spirits may not come. That’s part of dealing with something real and objective. It isn’t always 100 percent successful, because not everything is about you.
I didn't catch this the first time, but I really like this insight. It's not completely about the practitioner. Spirits are real (whether they're real parts of you or entirely objective entities or both). And, if so, they're not going to be compliant or available all the time. They're not going to be successful all the time. And so neither are you in this magical style (or, I imagine, in any magical style).
What to do? Suck it up and keep working. But understand that magic works with nature (and everything "nature" implies), not against or in spite of it.