"There is only one plain rule of life, eternally binding and independent of all variations in creeds, and in the interpretations of creeds, embracing equally the greatest moralities and the smallest; it is this---- try thyself unweariedly till thou findest the highest thing thou art capable of doing, faculties and outward circumstances being duly considered, and then do it."
---John Stuart Mill
This quote is a tall order but who can deny the truth in it, or how the world would profit if we all considered this when entering life as an adult. Trying ourselves to find out our capabilities is no small project in itself.
Balancing that with our faculties and outward circumstances, certainly the other half of the equation, takes a long hard look as well.