There are many excellent advice here so I'll tell you my personal experience with this issue. Hopefully that will help you.
I've been doing CrossFit for almost four years. I'm 30, male. It was a total struggle for me at first but after a few months I managed to finally do a WoD fully RX. I couldn't feel my arms at the end but I was super stoked. Anyways, then soon after I started to hitting my stride. I started going to our "club" (competitor) level courses and was becoming better and better. I knew I would never become the best, but I could hang with some of our best people. PRs were coming fast and furious, and I felt pretty good at hitting my goals regularly.
Then suddenly, the wall. This was about two and half years since I started. I don't think I PR'd or did ANYTHING better for six months. I was depressed. Started to wonder what went wrong and even thought about quitting. Ultimately I kept going because of the community at our gym, but still, I had minimal progress. The thought of quitting kept creeping back. Not too long after, I had to move due to a new job. That meant finding a new gym, new people and environment to train with. That's where things changed.
Slight tangent here, because it's relevant. I had knee surgery on my right knee eight years ago. I hurt it going to school, and the rehab process was the first time in my life I started working out regularly. (Those are stories for another time.) Due to my negligence during rehab, I never gained all of my range of motion back. Because of this, my left hip flexor was constantly sore and I had pains in my back and shoulder. Still, I pressed on.
Ok, I moved. New environment. New gym. And new physical therapist. I finally decided to see somebody about my knee. My therapist worked with me, gave me a few pointers, and basically told me to work on my air squat, one of the fundamental skills of CrossFit. Now, I don't mean to brag but I have a pretty good back squat. So this was total reality check to me. Good thing my form wasn't totally off and there were only some minor tweaks, albeit difficult, I needed to work on. I sucked it up and did. My squat numbers went down instantly. Not a whole lot, but