If you got here from an edit summary, the most important thing is: just because there is a citation showing that something exists doesn't mean that it qualifies for inclusion in an article.
Recently, I've been going through a PetScan query that tracks articles with {{Infobox YouTube personality}} in Category:Articles lacking reliable references, aka YouTuber articles that rely on primaries. The most common error, by far, is the tendency to write a statement and the only citation backing it up is just proof that the thing exists, or that the thing happened. Here are a few examples.
Person mantains a section on their website for answering questions
[ref = the questions page on their website]In 20XX, person released a new series of gaming videos.
[ref = links to episodes of the series]
There doesn't necessarily have to be a reference pointing to the thing either:
Person released a follow-up video the next month, although it ...
Here's an actual, non-made up example from here:
His acceptance speech for the award was notably curt, as he walked up to the mic, said "Thank you", and immediately walked off the stage.
[ref = a video of him doing just that]
Wikipedia's sourcing policy on biographies of living people is more stringent, and indiscriminate inclusion of trivial events only serves to bloat articles and give YouTuber Wikipedia articles an even worse reputation than they already have. I'm assuming that most editors on Wikipedia will not make this mistake; if you're one of those, keep a look out for this error if you're casually browsing some internet-y BLPs. If you're wondering what policy these statements violate, I would say no original research and undue weight, since it provides the same amount of emphasis as things that were actually discussed in secondary sources, and also make articles longer than they actually should be.
I wrote this essay for my edit summaries, to explain to editors why they're seeing a (−1,948) in their watchlist (and so I don't miserably fail at jankily explaining the error in every edit summary!)