A community with high levels of activity and a lot of members might appear a great success.
But in perspective, it can be a big failure.
For example, imagine you've been hired by Apple to build their official community. You gradually build the community to 15,000 active members. Would you consider that a success?
Apple has a HUGE audience of incredibly passionate fans. The total market size is massive, the passion is high, only 15,000 active members doesn't cut it.
This is where we have to see the success in perspective to the total size of the audience and their existing passion for the product. Oprah has hundreds of active community members, but with an audience in the millions – well, that's not good enough.
Some successful communities should be much more successful. Some punch far above their weight. But a highly active community alone shouldn't be the definitive factor of success.
There is a difference between doing well, doing as well as you should be, and doing better than expected.