Why were crystals seen in the flask after it was heated?

The flask then contains a hot solution, in which solute molecules - both the desired compound and impurities - move freely among the hot solvent molecules. As the solution cools, the solvent can no longer hold all of the solute molecules, and they begin to leave the solution and form solid crystals.

Ithink that the use of creativity in the sciences entails that one produce something out of nothing or from another thing. with this, i think that the he wrote down his results as four parts of the atomic theory is the manifestation of the  creativity of john dalton.