The Four Tendencies
Author Gretchen Rubin proposed in 2017 that we can be classified by how we respond to outer expectations (a deadline, a request) and inner expectations (a resolution, a personal goal). Upholders meet both; Questioners meet only those that make sense to them; Obligers meet outer ones but struggle with their own; Rebels resist both.
It's a popular framework rather than a scientific model, but it's very practical: knowing your tendency helps you design habits that work with your nature instead of against it.