I wonder if "hustle mentality" is something of an evolution the Puritan work ethic for a secular age? There's strains of Evangelical protestantism which place a great emphasis on the value of hard work to the exclusion of other parts of life, and Evangelicalism was extremely influential on Anglophone society for a large part of its history.
"People that are successful work hard" "I'm not successful yet" -> "Work harder" is a positive feedback loop train to burnout.
Maybe the real secret is "People that are successful work hard and have balance in their lives" but the problem is nobody knows what balance is. It's different for every person.
