Will Smith says marriage to Jada has been difficult, grueling but they refuse to quit

Will Smith has admitted marriage is difficult and grueling but the secret of being with his wife Jada Pinkett Smith is,they never quit on themselves.He spoke to Entertainment Tonight about how they keep their relationship so strong.  
                               'We've been married 20 years and we've been asking ourselves [what’s the secret to marriage] and really at the end of the day it’s just not quitting,' You can’t expect it to be easy,' It’s like our marriage was the most difficult, grueling, excruciating thing that we have ever taken on in our lives. And you know we're just not quitters. 'I would say is that we never went into working on our relationship,' 'We only ever worked on ourselves individually, and then presented ourselves to one another better than we were previously.'