In movie title "In Pursuit of Happyness" why is happiness misspelled?

The word "Happyness" in the title has been taken from the misspelling of "Fun Joy Happyness" on a mural children have painted on the Chinatown daycare center where Chris Gardner takes his son, Christopher. When Chris points out the mistake, Mrs. Chu replies that it is not important to the pre-schoolers how the word is spelled, only that they have happiness. This leads Chris to contemplate the inclusion of the concept of the individual's right to "pursuit of happiness" in the Declaration of Independence, and how to pursue a happier, more emotionally secure childhood for his son, than his own had been.

Pursuit Of Happyness Meaning

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It's explained in the movie. It is written outside of an Asian daycare as happyness. Will Smith's character comments on it.