According to the Great Commission - the measure of success is in both WHO is following (how many, people groups) and the DEPTH of the follower-ship (level of student, are they growing deeper). The Great Commission isn't successful without both of these elements.

For example, if one person becomes a student follower of Jesus, but measures weren't taken to allow ten people to follow Jesus at the same depth level (success is lost). The opposite is true as well. Lot of people who follow, but aren't growing into deeper students isn't success either.

Matthew 28:19