I know a lot of microstockers, having been involved in some way in this business for a long time. Where you start will vary depending on how you found microstock and the reasons you chose to get involved in the industry.
If you are a hobbyist photographer deciding to make money from your photos, you are going to find the learning curve steep. Things you probably considered: lighting, noise, composition. Things you NEVER considered: model releases, taxes, commercial value, series images, design.
If you’re a professional photographer already and jumping ship to microstock, you probably considered: business, taxes, branding, image quality. You never considered: rejections, noise, and the value of being really good at isolations & extractions.
If you are at all serious about microstock as a way to earn your income or even make a few dollars, you will get rejected at some point. Sometimes a reviewer on one site may get a full batch rejected on another site. In one case, at least, a reviewer got their own images rejected on the site they reviewed for! So yes, it’s going to happen to you.
People deal with rejection in their own ways - this isn’t going to be a diatribe on “how to get over it” or how to deal with rejections. You, individually, either will take it as “do better, try again” or “screw it, I’m taking my ball & going home.” You will *never* understand all of the reasons for rejections. We just yesterday had an image rejected on Dreamstime because it was a silhouette and I added a Model Release. You don’t apparently need a MR on Dreamstime for silhouettes (like you do other sites) so my image was rejected for: “Image does not contain a recognizable person, no model release needed. Please correct the issue and resubmit.” If I had not put a MR on Shutterstock’s upload, it would have been rejected for having no MR. If that doesn’t convince you that you will *never* understand 100% of your rejections…
Here are your action options when you get a rejection:
1) Quit microstock completely. Happens all the time.
2) Be angry, flail about a bit, post about it on some microstock forum or other. Fail to understand. Fail to improve.
3) Completely understand, actually praise the reviewer, and try again.
4) Put the image in a resubmit to folder and resubmit it.
5) Ignore the rejection and submit more photos, trying to get better.
Those are really the bulk of your options. Two are non-productive. Three have the possibility of being more productive. Rejections suck. Sometimes you have to decide to cut losses - and “quit microstock” but on a site by site basis. There will be some changes to my list next month, especially related to that particular topic. It does nobody any good to submit 1000 images to a site that isn’t looking for your work. At the same time, the only way to make money in microstock is to add more images, improve your quality.