As illustrated below, peptides 1 and 2 are capable of forming amphipathic helices with hydrophobic amino acids on one side and hydrophilic amino acids on the other. However, peptide one carries several negatively charged amino acids on its hydrophilic side and, therefore, is unlikely to serve as a signal peptide for import into mitochondria. Only peptide 2 carries a positively charged hydrophilic side on its helix and is likely to serve as a signal peptide for import of mitochondrial proteins. By contrast, EGF binds to a specific EGF receptor and is internalized by receptor-mediated endocytosis. These calculations, as alluded by the authors, make the point that by having specific tight-binding receptors on the cell surface, cells can take up molecules from their surroundings at a much higher rate than they could simply by taking in fluid.
Fishing provides an analogy.
You could fish by taking random net-fulls from a stream, and occasionally you might catch a fish. But if you put bait where you cast your net, you increase your chances of success enormously. Each time a molecule of EGF hits a receptor, it sticks and subsequently makes its way to a coated pit to be internalized. If the EGF were simply trapped like HRP, its rate of uptake would be infinitesimal at the usual in vivo concentrations.