"Marriage is like riding a bike or sailing," Ruderman said. "When one person moves and shifts, the other will move and shift in a complementary way. That's how we get our forward motion - and that's what gives a relationship life." "For a marriage to stay healthy," Raji said, "two people can't dig their heels in. If they can look for solutions without thinking they're giving up a part of their private selves, they move into a new dimension of adulthood." Conflict is as much a part of marriage as compromise, according to the experts, and successful spouses accept the need for it. "They have to learn to trust each other," said Lori Gordon of the Falls Church, Va., Family Relations Institute. "That may sound almost too basic, but the ability to confide intense feelings - of whatever kind - is necessary to emotional closeness."