If you have had a long and contented marriage or partnership (and I'll let each of you define the terms yourself), to what do you attribute it?

I see, among my friends and acquaintances, many very good relationships, many compromises and some very unhappy ones. Share your secret ingredients, if you will, and the length of your commitment. In particular, I am watching a couple in their early seventies; she is suffering with advanced Parkinson’s and her husband is a tender and cheerful caregiver. I watch them laugh and moan together without either partner appearing to be a martyr.