As others have said, the concept of "Successful" is an arbitrary concept that is determined by the individual's idea of what success is. But in general, I agree with what Crown said. Some people can make one video and that video can get viral. The magical formula for how to do this is a mystery to me, but in general, you have to do things that my integrity does not allow me to do, or you just have to be really lucky. But your average YouTuber has to work their butts off for a long time to build their channel, inch by inch, step by step, mile by mile. And just when you think you are going to make it, something can happen like the Adpocolyps of 2017 that can ruin your channel and set you back to square one.