A lot of customers think I can come in, fertilize a yard, and that will gaurantee success. I wish this was true, but it's not the case. A healthy yard requires coordination between several factor's, a few are: good watering, mowing, cooperation from pets, fixing and adjusting sprinklers constantly, and all of these done in a timely manner. Procrastination in 100 degree weather can be very detrimental.
I like to think of it like Barry Bonds. Barry was a great baseball player early on in his career. Later in his career he started using steroids (allegedly), and became an even better player. Like a healthy yard, Barry was already a great player. The steroids, like fertilizer, enhanced what was already there. Steroids don't give you natural athleticism, great hand eye coordination, or a good idea of what pitch is coming. Similarly, fertilizer won't make up for mistakes being made on other aspects of the yard. They will only make a healthy yard better