All in the Timing
Devarim (Deuteronomy 1:1-3:22 )
The Sages tell us that Moses did not rebuke the Jewish people until right before he died. They cite other examples of people who only gave rebuke right before their passing from this world - Jacob to his sons, Samuel to the Jewish people, and a few more.
Even though the idea of giving rebuke before one dies can only be applied once in a lifetime, the principle applies to other circumstances: I(f you want to give rebuke, you need to do so at a time of goodwill.
Accepting rebuke from someone is the second hardest thing in life. (The hardest is giving it!) The natural human tendency is to get upset and defend oneself from a perceived attack. The last thing that a person is likely to do is listen honestly and evaluate the rebuke. Because of this, it is imperative that one chooses a moment where the feeling is good to start with. Rebuke given at the best of moments is still incredibly difficult to accept; rebuke given at a time of upset and annoyance has no chance of being heard.
Right before a person dies, is a time of goodwill. But taking it down to a more day-to-day level, it is a given that if you want to tell someone off, you cannot do so when he is upset or you are upset - and certainly not when you are both upset! The natural tendency is precisely the opposite, though. When we are upset, that's when we want to tell the person exactly what we think. Once we have calmed down, we no longer feel the need to do so.
In marriage, for example, there are many times when it's important to tell your spouse that you think he/she acted inappropriately. Otherwise, the person will probably do it again, then you will get upset again, and once you've calmed down, you won't bother to tell that person - and the cycle will start all over. Either that, or you will speak out in the heat of the moment and your point will not be heard.
The key is patience. When you get upset with your spouse, first wait until you calm down - until you feel love for him/her again, until you can remember exactly why you married this person and why you would marry the person again if you were given another chance. From that place of goodwill and love, tell the person why you were upset. It's night and day different from doing it when you are upset - and the chances of it helping the relationship, rather than undermining it, are massively increased.