The biggest illusion is the power we assign to thinking. Our thinking mind has given us so many things but yet the belief that ideas come by thinking on them is incomplete. Ideas are ever floating in our mind we just need to be aware to catch those ideas. What is needed is the settling down of the chaos of ideas.
But the training of awareness in catching those floating ideas is very hard. So hard that it takes the form of untraining. Untraining because it is mostly the letting go of our learned behavior. Opposite of what is expected of a typical training where a certain behavior is reinforced.