The Secret Garden

by Frances Hodgson Burnett

At first people refuse to believe that a strange new thing can be done, then they begin to hope it can be done, then they see it can be done—then it is done and all the world wonders why it was not done centuries ago.

When new beautiful thoughts began to push out the old hideous ones, life began to come back to him, his blood ran healthily through his veins and strength poured into him like a flood. His scientific experiment was quite practical and simple and there was nothing weird about it at all. Much more surprising things can happen to any one who, when a disagreeable or discouraged thought comes into his mind, just has the sense to remember in time and push it out by putting in an agreeable determinedly courageous one. Two things cannot be in one place.

"Where, you tend a rose, my lad, A thistle cannot grow."

There is a lovely paragraph just before this too but this finely summarises the theory of manifestation and replacing old with new