Regarding social media, fan art and luck, I think it's important to be aware that getting "lucky" and going outrageously viral with a post, especially a piece of fan art, doesn't mean you're all set. It's not completely useless, but it's maybe not as effective a means of promotion as people think.
Because on the internet, when marketing, you need to always keep in mind this one concept: every extra click loses people.
Only a fraction of the people who see the piece on their timeline will drop a like, comment or share.
Then only a fraction of them will go to your profile to see that you have other work.
Then only a fraction of them will be interested enough to look at your original work (how many depends somewhat on how similar in style, tone, themes and audience demographics your work is to the thing you posted fanart of).
Then only a fraction of those will follow links off the platform they're on to look at a comic.
And then only a fraction of those few who got this far and looked at your comic will subscribe and become readers.
It's compounded nowadays with the way social media is constructed to make leaving the site a pain. Twitter's algorithm doesn't like links, for example. Social media platforms don't want you to go and look at somebody's webcomic on Tapas; they want you to stay on their platform and engage with more posts there. This means they're a lot less effective than they used to be for promotion than they were back in the day.
I'm friends with a lot of professional artists, and a general feeling is that fan art can boost engagement and your social media following, but you need to go in knowing that most people who engage with your fan content won't then engage with your original content. It's not a good way to advertise your own stuff, but if you pick the right fandoms, you might be able to attract the attention of people who like similar things and then you can market your original content to them while you have their attention, and whether that succeeds will depend on how suited your content is to that audience and how well you market it, just as if you were advertising anywhere else.
In many cases, you may find that it's just as effective, if not more, to post some panels from your comic that highlight how funny or dramatic your comic is and to tag it into every webcomics-related or other appropriate tag, as it is to draw a really great piece of Owl House fanart that gets a thousand likes and then to hope some of them look at your other stuff. In either case, whether people engage with your original content depends heavily on how accessible, appealing and engaging your original content is. At least the people browsing webcomic tags are likely to actually be looking for webcomics to read and will be open to giving original content a shot; the people browsing Owl House tags probably aren't, so even if the engagement with that post is high, the trickle-down into new readers on your original comic might be very small.
So that's why I don't really encourage people to focus too heavily on the "luck" element of things, because it's simply not the case that one big viral hit will have you set (or even several if you're me... I once went so viral I got interviewed by Kotaku. There are multiple blog entries about pieces of viral content I've done because one is used as a teaching aid now). Once you have people's attention, the thing you show them while they're looking at you needs to be accessible, appealing and entertaining just as much as if you use or are gifted any other means to get people looking at your work (ie. paying for ads, getting a Tapas feature, having a famous person give you a shout-out). Having a massive number of people looking may offset your poor "conversion rate" (an advertising term: Conversion is how many people who see an ad click to go to the site, or how many people who get to the site subscribe or buy something), but only somewhat. So you should always be focusing on how to make your work as inviting and engaging to the people who do see it as possible, before you focus on trying to make lots of people see it.
You can't necessarily control when your visibility gets boosted by a feature or a recommendation or something, or how well suited to your original work the people who see you are, so yeah, that part is luck... but you can control how you capitalise on that luck by making sure that what people see of your original work when it's visible looks attractive and compelling, and that's nearly entirely not luck (the only luck element is if you happen to work in a fashionable style and genre without having deliberately planned it), it's largely stuff you can choose and learn through research, study, attention to detail and good creative choices. If your work isn't grabbing people's interest when people see it on the forums or discord or webcomics communities, people seeing your work because you drew fan art isn't going to fix that problem.
