I worked as a chemical operator doing organic chemical reactions. The first time I had to crystalize a chemical which was in its present state dissolved in a solvent the writeup told me to cool it to a certain temperature; but it didn't crystalize. I went to the process chemist because I thought I had made a mistake somewhere and he laughed and pulled a small bottle out of his desk and said to dump this in. He called it "seed". He said that the chemical needed to "remember" the crystal shape. This shocked me. The idea that a chemical needed to remember the shape of the crystal we needed it to form was a shock to me. Fascinating to think in that way about chemical reactions.