The mind denies seeing the things directly, to be them present without the word and the symbol.
You for instance say, that the sky is blue. The one who hears it, interprets it from the conception he has about blue and reproduces it to you in his own code.
In that way we live in symbols, and dreams are a part of this symbolic process.
We are not able to perceive directly and immediate without the symbols, the words, the prejudices and the conclusions.