"How often could things be remedied by a word. How often it is left unspoken".
(Norman Douglas, British novelist)
In marriage, many of us are quick to say a thoughtless or hurtful thing but slow to apologize for it. It's understandable, of course, that when we're sufficiently provoked we're going to want to lash out at the person provoking us. But too often we go overboard. We punish a petty offense with a cruel remark ("I can't believe anyone could be so stupid to forget to pack sunscreen on a trip to Aruba"). Or we become obsessed with the need to prove that our spouse is wrong and we're right ("Will you ever admit that your parents have been manipulating you all these years?"). Or, instead of addressing the specific issue at hand, we dredge up vague but emotionally-laden complaints from the past ("You always put your needs first").
I'm not so naive to think that people will ever stop saying these kinds of things when they're angry, exasperated, or just plain tired. But hurtful words have conseqences---often far-reaching consequences---if they are not followed by a sincere and relatively swift apology. Plenty of divorces have their roots in insensitive remarks and bruised feelings.
You would think that it's no big deal to say, "I'm sorry about what I said. I'll do my best not to say that again". But some people would sooner walk barefoot on broken beer bottles than admit that they're wrong. In fact, they never even think they're wrong. They're not only "right", but they have to be acknowledged as being right. People like that have a stubbornness and false pride that can seriously threaten a marriage. A successful marriage requires compromise, and compromise requires a sense of proportion, a sense of humor, and a respect for the other person as an equal partner in life.
If you're someone who has always needed to be right, you've got to decide whether it's more important for you to be right or to be happily married. If you really care about your marriage, learn to relax a bit and not get hung up on every little thing that goes wrong. And learn to say you're sorry, and mean it. Otherwise, the day may come when you won't have anyone around to argue with, or feel superior to.