What does it mean when my espresso pours very quickly with light color?

This is called under extraction, which occurs when too little of the essential oils, flavors, and colors from the coffee grounds have been extracted. The resulting crema is thin with a creamy light brown color that quickly dissipates, and the espresso tastes sour and acidic. To fix this, use a finer grind, add more grinds (one cup: 10-12g, two cups: 20-22g), or tamp the grounds more firmly with 20-30lb of force for freshly ground coffee or 30-40lb for pre-ground coffee. (Page 10-11)