What's the minimum threshold a story must reach for it to be considered "successful"?

I think currently it's pretty vague, like, obviously, a story with 3k following would be considered successful and it pretty much is. But what are the baseline stats that are to be reached for a series to be considered 'successful'?

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Naturally, most of us authors may not be part of that squad, but having a clear enough line to walk towards is fun nonetheless. So, do provide your opinions on the matter.