Long-term intimate relationships

So I am finally starting my blog 2, for which, my topic is: What are the secrets of a "good marriage" (or long-term intimate relationship)?

So the textbook explains that a successful relationship begins with passionate love. Passionate love includes strong desires, excitment and feelings of longing for another person. The tricky bit then can be transforming passionate love into companionate love, which is calmer and is perceiving your partner as your best friend and soul mate. Companionate love signifies commitment and so is essential to long term relationships (pp. 360). Therefore, a high incidence of divorce could be due to difficulties in creating companionate love.

Sternberg's triangle tries to explain contributors of successful long-term marriages. He believes relationships are made up of three components; passion, intimacy and commitment. All three are needed but in different ratios can produce different types of relationships.

What does everyone else think is the most important contributor to a successful long-term relationship??