I definitely don't think there's one definitive answer. Many current Youtubers have been around when they hopped onto Youtube and their personalities weren't really prominent on the internet. While it's difficult to get noticed now, I think the most important factors that contribute are your motivation, your outreach and your quality of content. If you boil it down to those three, those are key to generating a well established business.
Someone mentioned how Markiplier treated his channel like a business - and that's exactly it. You can produce content a lot, but the content has to be quality assured so that the audience is getting what they subscribed for. After that your outreach is super important. Are you networking with others? Have you made good friends with people who can push your business up? No? Then you probably won't get far. Just like acting, painting, business students, etc. You have to network in order to get yourself somewhere. Some may get popular by sheer luck, but that's literally such a low chance.
Finally there's motivation. And the key thing is to have motivation TO create that quality content. Many youtubers just create content because it's fun and it's a great creative outlet. Which is absolutely great - I do that, we all do that. But in terms of a business standpoint, you have to be motivated to push yourself to the best. This means tweeking, editing, strategizing, etc. on how to do better outreach, how to do better videos, etc.
Obviously there are other key factors important to popularity such as your personality, or what types of videos you make. But those 3 are what I find many Youtubers strive for.