A few years ago, I wanted to do a webtoon, but I didn't know how to draw, I relied on my best friend to do it, he's a good artist, but the guy really made every excuse under the sun to not do the work, the rare occasion when he started the work, he'd lose motivation due to a myriad of reasons, then he finally gave up on his art dreams, fastforward a few years, and I learned how to draw, nowadays I'm more skilled than he was, and I'll never trust people in collabs again.
(I forgot to mention that this also happened when I was in highschool with an ex-colleague, a lot of artists lack motivation, or have low self-esteem, it seems.)