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

[luinil]

A couple of factors,
1) Did it live up to sales expectations?
2) Did it turn a profit for the game companies?
--How much of a profit?

The bigger the profit, the bigger the success. With the exception being when the sales turn a tidy profit, but still don't live up to sales expectations, people will not always consider it a success, even when it is.