On Stack Exchange Networks, sites are called "communities". I have observed that many users (let's say N) come to join the site, several of them (S=N-100) stick with site for a while, very few of them (F=N-500) spend more time to learn and get engaged and even less of them (L=N-1000) make very useful contributions to the site and also help guiding new users.
One of the important thing to be noted is that after joining the site, little numbers (L) start learning more and more and the knowledge gets saturated at some point (that doesn't mean there is no more thing to know but that means at one stage one won't find enough interest which s/he used to enjoy while learning the things). So, after reaching the state, users may gradually start losing the intensity of interest and may become less and less active. That may lead users to become inactive on the site.
Now, the point is that the number L should be balanced in order to keep the site productive.
How do you balance it to avoid the chance of getting the total number of imp users (L1) becoming inactive more than that of new becoming imp (L2)? I.e. how to keep experienced users active on site or encouraging new users to learn and grow?
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