I want to start by saying that explanations have their place and sometimes they are important and necessary. But sometimes there are too many explanations. And it can sometimes do more harm than good.
Let's take an example. You forgot to call a friend you promised. Once it hits you, what do you do? Do you say sorry, I forgot and add an explanation? Is the explanation/excuse reasonable, or do you add it to cover up the fact that you actually forgot? Common and very human thing to do.
But… when you explain, it starts to be about you. The recipient doesn’t always feel the excuse. You think the explanation is a part of the excuse, but often it's mostly about you protecting yourself, covering up or making yourself look good.   
Explaining can easily become an excuse to avoid taking responsibility. It’s not you who made the mistake, there is an explanation, a reason why it turned out the way it did. As a recipient, it doesn’t feel good. A better response is to own the mistake and just say sorry, I made a mistake. It is straight-backed and genuine.