Question anyone wanna answer?

So...I'm in graphic design, right. And we all know stealing someone else's work and saying it's yours is plagiarism, right? Yes, right. But here's the thing my teacher points out "If it's not your own character, and you sell artwork with that character, that's plagiarism." ....Ok, so basically what you're saying is that us artists can no longer create work, because to tell ya the truth, all of our inspiration comes from things already made, that's how we humans work. I know PLENTY of artists who sell their work, and they use characters they have no copyrights to...YET THEY DON'T GET IN TROUBLE! -_- What's with that?! Seriously, if we can't use a character, then no one should be artists. Because to put it bluntly, all of our "original" things are just things our brain slightly remembers from different inspirations. 


The illustration is Link and I'm making it with him fighting. Yes, it's quite obvious Link is copyright of Nintendo, EVERYONE knows that. I'm not claiming him as mine, I'm claiming the ARTWORK THAT I PUT TOGETHER AND DESIGNED MYSELF as mine.........I created everything in the illustration, from poses to characters. I even went through the enemies I have and made them my own with some of my own designing....so why can I still not claim the illustration as mine? 


See what I'm getting at...?