There's a whole lot of stuff that goes into how successful I think my work is.
The social aspect is pretty important, especially these days: how many people are actively interacting with you and your story via comments, likes, questions, fanart, etc is a good indication, at least for me, that people are invested/interested in what I'm doing.
The monetary aspect ((conventions, Patreon, etc)) is always on my mind, being in the art industry. While I've been able to make a living working at studios and doing freelance contracts, my goal is to eventually support myself comfortably on my own work. Every step in that direction is a good one! C:
Most importantly though, at least to me, is looking back and seeing how much I've done. It's having the self-discipline to put out a page every week, or at least do your best to maintain updates. In the past I've had trouble finishing projects or not even starting something in the first place. However I've been steadily working on Shanties for a long time now, long before I started uploading it on Tapastic. Knowing that I've made it this far and have no intentions of quitting already makes it successful in my mind. It's a personal success, even if nothing else comes of it.