Well, normally we have a low concentration of that primary messenger. We can have as low as a single molecule that binds onto that receptor, onto that transmembrane protein. And even though we only have this single primary messenger, what happens inside the cell is we produce many of these intracellular secondary messengers and then they can basically go on to carry out their individual processes. And this greatly amplifies the overall effect of this information. So we see that these secondary messengers, this step basically amplifies that signal. Now, once secondary messengers are produced, they can easily diffuse across that cell.