It sounds so cliche, but communication is the backbone of every good relationship. You need to know how and be willing/able to talk to each other about everything from what to have for dinner to dealing with huge issues like death. If you aren't ready, willing and able to communicate openly and honestly all of the time, it will never work.

i am 62 wife 67 been married 36yr was a blind date have no idea it just worked

ROBERT:
I'm sure you've worked hard at it over the years. I think it's great that you met on a blind date though. You're proof that they sometimes do work out!