In the ego mind, the mind is split, and so is your will. You have willed against yourself. So now your mind has more than one will in it, seeming to act in contradiction. You are at war with yourself.
So what happens now is, your will attempts to still "cause", but then this other opposing will also attempts to "cause", and the two of them are opposite each other in every way so this "cancels out" all of the possible effects.
It's like being constipated, or a stalemate. We literally basically STOP ourselves from willing anything at all. This is why we do not produce and EFFECTS. This is also why, in a split mind, it seems like we cannot have any power over the world or use the mind's power to make anything happen directly. We're stuck in a body that seems to be cut off from the environment and our mind seems totally powerless.
When the will is reunited as whole and is not divided against itself (no ego), the mind no longer has opposition. It is able to now be single minded and to will consistently in one direction. This unopposed will has the Power of God, to CAUSE, AND to produce effects. This unleashes the power of the mind to manifest. It was in this state that we originally made the universe appear.
This is also a key in miracle working. Miracles don't work in a spirit of fear, and fear comes from separation, meaning that if you are afraid that "the miracle wont work" or "the symptoms aren't going away" or "I don't trust this power" or "I don't think I can do this etc"... the perceived "things that would oppose success" are actually other aspects of YOUR OWN WILL in your own mind, in conflict with what you're trying to achieve.
This is why when the mind and will are split, there are no miracles happening. Something has gone wrong. The mind is literally believing in an opposing will which it thinks is "out there" or is alien to it or external to it. It is not. It's inside your mind. So when you are "against yourself", you are literally stopping your will, against your will. And so you cancel out the effects of what you try to make happen.
A mind which is whole does not even regard the current state of the world, appearances, how severe a problem seems, how big the challenge, whether it's healing a headache or moving a mountain. When the mind is clearly aware that it has ONE WILL, and there is no opposing will (because nothing happens against your will, therefore everything happens BY your will).... it is more like... an artist painting new brushstrokes. The canvas does not resist the paint. There is nothing stopping an entirely new projection from happening. What was there before has NO POWER to stop the effects from showing up.
This is why in miracle working you do not "ask" stuff to go away or be healed. That is evidence that you believe there is a will opposing yours (physical matter? sickness? causes?) which has the power to stop you, therefore you have to "ask permission" for it to change. That's not how miracles happen.
Also you will find it's useful to "command" that something change. If you are certain and authoritative and whole-minded/loving enough, it must comply. But the fact is, you're ultimately not even commanding a "separate thing" to change. In your truest nature, you simply EXPRESS. You CREATE. Stuff just comes out of you joyfully and, if that means making forms, then the forms just instantly show up and materialize. Not because you asked them to, but because you simply created them.
To work miracles we must UNDO all belief that there is any cause in the world, any power over you, any alien will, any separate strength or reason or order of difficult that suggests "it might not work because" or "thats too big a challenge" or "it appears to much a problem."
I'm reminded of star wars, where Luke is being taught by Yoda, and believes he cannot lift the spaceship from the swamp because "its too big". That's the hierarchy of illusions. Yoda then demonstrated that size does not matter. Effectively he was demonstrating the miracle-working power of the mind.