Any time your brain is getting bounced around CTE can develop. A few things contribute to this: measure of impact, frequency of impact, and genes. Some guys can live to almost one hundred, speak coherently, and knock out muggers with their bare fists (read up on Jack Dempsey). Jake LaMotta looked like a shameless slugger, but he could slip better than he was given credit for, and plus, after all those fights, his brain held up too. In the 80's he was old, but still well-spoken. Genes go a long way. Muhammad Ali wasn't in as many fights as other guys, but fate had his number. He got Parkinson's and who knows if it would have simply developed later in life had he never boxed. Michael J. Fox was never a fighter and look at him, regrettably. Genes are a factor, but how you fight, goes a long way too (same reason some people can smoke for years and run miles against a healthy pair of lungs that can't keep up - just genetic). The two go hand in hand. You know what they say about each individual fighter: you've only got so many fights in you. There's something to that. Knowing how to diminish a punch, rather than let it land full force, helps. Size of gloves helps (bigger guys spar with 16oz gloves), and anybody that says it doesn't should ask themselves why boxers admit to feeling the difference in power and effect when the glove size varies.
I'm reticent to say that head gear doesn't help. Get the right kind of head gear for your skill level and purpose. NEVER or DON'T are strong words, especially when it comes to one individual taking what works for them and projecting it onto others. Even high level boxers will use certain head gear, and it's not because they want a sense of false safety. It's not what you use, it's how you use it. Find a piece of head gear that suits your needs, but don't accept it as part of your defense. That's imprudent. You don't buckle up before you drive hoping to get into an accident, right? You be proactive, because that's what you ought to always be.
So, short answer: spar smart, accept that you will get hit. You have to make friends with the fact that your brain is going to get rattled like an etch-a-sketch. That doesn't mean you can't try to fight smart, just don't fight scared. If you can't handle that then you like the idea of striking, but not actually doing it. On some level you've gotta make friends with the pain.