And that's to keep that protein, the polypeptide, from actually being washed away. Because as we add each amino acid, we essentially wash our solution to basically remove all the unwanted things from that solution. And so we want to anchor that growing polypeptide and keep it in place. Now, the second important point of the solid phase method is we have to use different types of molecules, activating and blocking agents to basically promote that particular reaction, the formation of peptide bond that we actually want to form. So in step number one, in order to promote and increase the specificity of the reaction and decrease the number of unwanted products from actually forming, we have to use these different types of molecules to direct the correct synthesis of the protein. Because remember, in any given amino acid, we have different types of groups and these different types of groups react in different ways.