I think this is a big reason for millennials that follow the negative stereotype. It's not the positive affirmation, it's that they've grown up being told by authority figures, including some very successful people, that they can do anything they put their mind to.
The vast majority that believe that and never stop to question it are doomed to fail. We're not all Bill Gates because it's more complicated to get there than just "trying harder".
Thanks for your comment! I can see that happening: instead of educating young minds to assess their comparative advantages in life, they are more often encouraged to have unrealistic dreams before a realistic roadmap.