The belief that abilities and intelligence can be developed through dedication and hard work.
If you failed, it's because you didn't believe in yourself hard enough.
"Let's approach this with a growth mindset." (Translation: The project failed but it's not a failure, it's a learning opportunity, which coincidentally doesn't require severance pay.)
From Carol Dweck's research, which was nuanced and interesting. Has been simplified into a corporate bumper sticker.