Collecting master sets is subset pursued by some SetCollectors. A master set contains all cards issued in a given product. This includes all inserts and parallels. With many modern sets there is a plethora of low numbered ParallelCards and even One of One cards, which makes a true master set difficult to obtain. Many collectors modify the definition to include everything numbered above a certain number, or focus their master set ambitions on products that do not contain the incredibly difficult parallels.