How many copies does a game have to be sold for it to considered successful?

[Rock_on_2008]

^Yeah this is the question I would like an answer to.

Does it depend on how well previous instalments have sold in the series if its a sequel? Say a new game (non-sequel) is made. How many sales is considered to be successful? Say a total of  500k or one million copies sold world wide? Sales of games are definitely not in relation to review scores some of the better games have struggled to sell 2 million whereas shovelware games have sold a lot more. Say a Halo game, MGS game and Mario game have to sell 7 million. Both GT and Final Fantasy games must sell over 10 million copies.