What must be encouraged and believed in?

There is almost no limit to the possibilities of the imagination, but to get its full power, you must trust your imagination. 

If you say to yourself constantly, as the mother says to the child—

But this is only play; this is not real, you never can make real the things you have created in thought.

The imagination itself is like a child, and must be encouraged, and believed in, or it cannot develop and do its perfect work.