Donald Trump is not beating Hillary Clinton in the polls, no matter how many times he says it
Donald Trump legitimately does not care about what polls actually say; he cares about what he can say about the polls.
He likes to talk about polls because polls are usually pretty good for him, at least since last July when he stormed into the lead in the Republican field. Polls serve as validation for his dominance, and so he talks about them as a slightly more subtle way of calling himself a winner. Last September, he suggested that he put so much weight on the polls that if his support started to crumble, he'd drop out. Obviously that didn't happen.
There's one set of polling that Trump likes to talk about, though, that is at odds with this pattern. Trump frequently talks and tweets about how polls show him beating Hillary Clinton, when in fact polls almost always show the exact opposite.
https://www.washingtonpost.com/news/the-fix/wp/2016/03/24/donald-trump-is-not-beating-hillary-clinton-in-the-polls-no-matter-how-many-times-he-says-it/