One thing that's present in every single spell or energy work etc. is psychology. Magic can be boiled down to pure will and intent. This is why every spell tells you to focus and meditate on your desired result(s) and may be extremely elaborate in its casting instructions or incantations/chants/prayers.
Thinking in the simplest terms of logic, despite what many people say, you can indeed influence the universe through sheer will power. Magic proves this and everyone who's ever cast a spell successfully knows this whether they believe and/or accept it or not.
Most anyone who's been practicing for long enough will tell you that you don't really need supplies to cast a spell. In truth, if you do use things from a spell's ingredient list, follow the instructions flawlessly, and do anything extra to aid the process, you will have a higher chance of success since you've thusly entered into a powerful enough state of mind in which your will can be more effective in producing results.
Think about it as a set mathematic equations:
Spell alone = low success rate
Spell + some intent = low to fair success rate
Spell + strong intent + all appropriate materials = fair to moderate success rate
Spell + strong intent + materials + true to casting instructions = moderate to high success rate
Spell + strong intent + materials + true to instructions + meditation, ritual robes, good timing with moon phase correlation, etc. = high success rate
*Note: These are simple examples which some may not feel apply to them. Nothing is set in stone as there are some exceptions to these equations.
This isn't to say that this is absolutely the way things are, rather this is the way most things pan out. This is why many people whose spells fail are told to keep trying or try extra techniques such as meditation. The veterans know what they need to do in order to be successful when casting and will tell you exactly what they think you're not doing (whether they put it in that manner or not) and how doing it will help.
This will and intent and even belief is not always a conscious thing, though. For highly logical people who believe more in science and/or what they see, hear, or otherwise experience, the concept of willing something into existence may seem quite ridiculous no matter how much their conscious mind wants to accept and utilize it. I used to be this way. Whenever I tried energy work, I wanted so badly to believe, but there was always that logical hint of doubt which destroyed any potential success and throwing all of my work and concentration out the window.
This works both ways. Some people who claim magic to be fake may have a small "just maybe" streak in them which could allow them to perform spells if they'd only give it a chance. Refer to Dr. Seuss' "Green Eggs and Ham" for this concept. The unnamed character is constantly offered the titular dish by Sam-I-Am, to whom the character denies many times claiming not to like it. Once he does try it, however, He finds he likes green eggs and ham. While the moral of the story is, in a nutshell, "Don't knock it before you try it", it can also be interpreted as "Just because you don't think you can or want to do something doesn't mean it's not true on the inside". One could argue that the unnamed character's liking of green eggs and ham is a latent unconscious liking which was only brought to light once the meal was given a chance to be experienced by the conscious mind.
Another aspect which is very much present in psionics and most energy works in general is "feeling" energy. Many will complain that no matter how much they try, they can never feel their energy. Many will also say that the feeling is purely personal and may be perceived in many ways from person to person. Biofeedback is a term used in relation to this. One definition of biofeedback is the body responding to the person's will by perceiving this energy flow or the desired intent. This again circles back to will power and how it effects the world around us.
The main point of all this is the one underlying element present in all magic and energy work. Your will is power. The stronger your will, the stronger your power. The stronger you believe it, the stronger your will. the stronger your state of mind, the stronger your ability to believe it. The stronger your adherence to rituals, instructions, and other elements of aid, the stronger your ability to believe it. Finally, the stronger your intent to cast a spell and get the desired results, the stronger you'll want to adhere to the instructions. Will is a synonym of intent. Thus, the circle is complete.
[This was written for people to understand magic on a psychological level, potentially turn skeptics into believers, and inform the beginner masses why their spell(s) didn't work. The writings here are based on largely accepted concepts from many different paths and crafts put into logical terms to accomplish these goals. It is not the intention of this post to change anyone's views, but merely to give them another point of view on which to ponder. Magic and energy workings are real crafts and should have real explanations just as any skeptic would request as proof. These are my views and I'm sticking to them, because I believe that this is truth to the best of my knowledge and experience. This article also takes no particular religion into question, as the last thing I want is to create a religious debate over ethics, teachings, or beliefs on how magic and/or energy works. As I said before, these are my personal beliefs, and you are free to interpret this information as you will.]