Ngtjyty

After reading that a Mary-Sue often is a projection of the author, I realized most of my stories are.

Is it a bad thing?

My MC aren't Mary-sues (at least I hope so), they're the opposite of perfect and always succeeding: I focus on flaws and illnesses, making some bad decisions, paying the price and regretting them, running away from their responsabilites, etc.

But in most of the time, "how my MC would react to this" or is very close to "how would I react to this". However this is only true for the setting, and character development is quite different.

I've also found a bunch of questions (1) (2) asking how NOT to do it, making me think it's something I should avoid even more.

Is there something inherently wrong with it? Does it make my story less interesting to read?

Self-projection into one's stories is an inevitability. Whose lens affects your outlook on life, and thus the worldbuilding/tone of your novel? That's right, yours. Who is the only person you have direct experience of the thoughts of? Once again, you.

As such, you shouldn't be surprised or beat yourself up over the fact your characters take on some, or even many of your traits. The question is not whether or not you share traits with your characters, but your intent behind it; believe me, it bleeds through.

If you're writing to have an escapist power-trip fantasy with people you think you'd like, then you're writing a mary sue, and it'll be obvious to even a slightly discerning reader (even the ones simple enough to think powerful/skilled characters alone are mary sues).

If you're writing to tell a story with layered, flawed characters to explore a theme through arcs and exploration, well, it'll show. It doesn't matter how incestuous the character soup is, if pretty much every character inherits something from their creator; as long as they are distinct enough to stand out and explore what needs to be explored, then you should be fine.

Mary-sue call-out culture has wracked poor folks like you with fear, and frankly, that isn't cool. I wrote an essay on this topic (it might be a tad rambling in hindsight) that can be found here:

https://storiesfromsekai.com/2018/06/17/critical-essay-the-checklist-effect-how-the-mary-sue-label-killed-creativity/

In addition to Matthew Dave's excellent answer..

Whether a character/story is interesting or not is more about the character/story themselves rather than where the inspiration for it comes from.

An author projecting themselves onto a character is not automatically going to be boring, if they are projecting interesting traits and elements onto the character then they are going to be interesting.

Something that gets very tiresome is when every (or at least most) of the characters are variations on the same projection but that doesn't sound like what you are doing. If supposedly different characters all behave/react in the same way that doesn't work.

A "Mary-Sue" can be a problem (depending upon execution) - but that isn't really because it's a projection of the author - they tend to be more idealized projections rather than realistic ones (i.e. they are who the author fantasizes about being in the story) and it's the idealization part rather than the projection that is the problem. A well-known example is everyone's favorite Star Trek chew-toy Wesley Crusher who was seen by many fans as being a Gene Roddenberry playing out his day dreams with a Mary-Sue archetype of himself, complete with insane amounts of contorted Wesley-saves-the-day plots - it's not until Roddenberry took a step back from the show that the character experienced actual development and real adversity (that wasn't just "Those dumb adults don't appreciate his genius")