Difficulty and effort are independent. Some people try to do hard things. Some people don't try to do easy things. Outcomes depend on difficulty, effort, and other factors.

Talking about measuring conscientiousness means part of the Big 5 model usually. Did you have in mind a different system for assigning people conscientiousness percentiles?

Do you often say COVID-19 really does seem like the lowest x percent of the population by SpO2?