A recent episode of No Such Thing as a Fish reminded me that flossing is linked to heart health and longevity (e.g., this study). That lead me to buy some interndental brushes and... not use them.
Later, I read The Wealth Ladder by Nick Maggiulli. It had a section on investing in your health, and it also talked about the link between flossing and longevity and heart health.
For the past year or so, I've been articulating to myself that "I want to have time and energy for the people I love." I was reading this book to help figure out what I want the rest of my life to look like.
In this context, the information finally hit me in a way that made me want be a person that flosses.
There's a field of study called identity-based motivation, that helps explain why this identity-oriented shift has actually sustained the flossing habit since I started a few weeks ago:
When action feels identity-congruent, experienced difficulty highlights that the behavior is important and meaningful. When action feels identity-incongruent, the same difficulty suggests that the behavior is pointless and “not for people like me.”