-80% of income variation is explained by country of birth and by family of origin. The rest is not all effort, as it includes gender, race and other factors related to luck.
-Most probably, all those in the classroom (students and lecturer of a Spanish public university) including myself belong to the richest 5% in the Planet.
-The richest 10% in the world is on average 80 times richer than the poorest 10%.
It seems to me that it is useful to remind students of the basic facts of the world we are in.