I have wondered about this question for a very long time. The other day the YouTube KSI had a massive rant about this on snapchat and it had a lot of meaning to it. KSI stated '' becoming big on YouTube is probably impossible'', but if you think about it their are thousands of people on YouTube creating content and any video could go viral unexpected. I personally think that if you work at something you can achieve and in this day an age anything is possible, but luck can be a BIG factor. Just keep at it and you never know. It might happen in a week... a year ... or never but you will never know unless you try. So dream big or you will limit your self.