There are only four kinds of people in this world: those who have been caregivers, those who currently are caregivers, those who will be caregivers, and those who will need caregivers.

Rosalynn Carter (b. 1927) American First Lady (1977–1981), and activist

Helping Yourself Help Others: A Book for Caregivers (1994; 2013) [with S. Golant]
    (Source)

This quotation is usually attributed directly to Carter, but she is actually quoting an unnamed caregiver colleague of hers.