I think we all come into fandom, not only with different life experiences (mine tend to put me in the cult of nice) but into different environments of fandom. The point where I got into actively participating in fandom (and producing fanworks myself) there was a bit more room for reviews than my current place in fandom has. When I started vidding poison_pagan was posting her reviews to vidding and even though she would often say negative things, I was eagerly looking forward to her reviewing one of my vids (she announced she wasn't going to watch any more QaF vids before she reviewed any of mine). In fact, she inspired me to start my own vidding critique journal, I never shared it with anyone and now I'm really glad I didn't because, quite frankly, I didn't know what I was talking about. I just knew what I liked and what I didn't, I couldn't articulate why. I feel I've gotten better now (although, I'm by no means a vidding expert) so I also occasionally volunteer for the_reel and am a member of vid_critics (although I haven't participated there yet). (Random question, are there such comms for fics? Since I'm not a fic writer, I've never seen or looked for them, but I'm wondering if vidders are just different).
The thing is, I can remember my very first "in depth" review I ever received. There was a feedback exchange on vidding and exsequar got my vid The Otherman. I can honestly say, that review (which is here if anyone is interested) changed the way I vidded. Even though I had done mostly POV vids up until that point, I had never *realized* that I was doing POV vids! exsequar brought that up, she kept mentioning POVs and how I would randomly change the POV and I realized she was right! I did that all the time, because I wasn't thinking of POVs when I was vidding! It was such a basic thing that I could have picked up had I read any meta on vidding, but it had never occurred to me. All my vidding knowledge at the beginning of my vidding career came from watching other people's vids. I knew what I like and what I didn't and I stupidly thought that would be enough.
I think it can probably be worse with writing because we all write every day. We all had to take it in school, we don't think we have to go and research how to do it. Which is why I think critical feedback and reviews are great. They give creators a chance to experiment and have the information come to them. Have the information personalized to their styles and delivered right to them. They give the creator a chance to see other people's reactions. And, they give the reviews a chance to articulate things to better understand them too.
Most of us have betas but sometimes it's a matter of having a *good* beta. Sometimes we choose our friends to be betas, friends who can't tell you when things aren't great. Or don't recognize when things aren't working. I know that when I first started vidding, I'd show my vids to carr0ts1979 but she was more of a cheerleader than a beta. Once I started seeing more critical reviews, especially of my vids, it made me go looking for vididng meta, it made me want to become a better beta myself. Had I not been involved in such an environment, I'm sure my vids would never have improved (well, I *hope* they've improved!).