In zazen, the mind gets tremendously resistant and thoughts will intrude immensely. We cannot fight the mind, it has had a life-time of conditioning, some believe that is also has previous life-times of conditioning. I prefer to look at NOW and see this enormous "mountain" in front of me, that is probably etched into my genetic memory.
We are looking at a universe with the small space of awareness of what is left to us, that is the Self. Perhaps sharing with you may help...
I get the incessant voices in my head, but there is a small space that can look at those voices and by connecting with that space, it will expand. Slowly or sometimes not so slowly. Sometimes profound and sometimes not so profound.
When the mind is overpowering, I give up and go with it. I deliberately "choose" to have it the way it is. Thoughts may racing around and around. What I have to do today, what I wish I had done or not done, yesterday. By choosing it as it is, I am making it happen, rather than having is happen to me. It's a paradox.
We cannot reach that space of Self as conquerors. We have the long and hard lesson of learning to be patient as we wait for it to come to us. Giving space in our awareness to let be whatever is there, whatever is being. It is totally in the present moment. The mind can only operate from past conditioning, even if it has the illusion that it can form the future. The past and future is never present, it is therefore an illusion.
Enlightenment and Self awareness can only come in this way. It is not created in the mind, because it already exists in all of us and encompasses the mind and all it contains - all the racing, random, trivial thoughts. It is IN our Self (awareness) not encompassing our Self. Self IS awareness.
Sometimes when the mind seems to race around, a question like, "who is watching all this racing around?" can be quite revealing. It is important not to look into the memory, or rationality and to keep discounting whatever the (rational) mind will answer. The only answer that is left then is emptiness. There is nothing (no-thing) there! As self is not a thing.