Unnecessary excuses
I am not going to talk about excuses about why you came late, why you didn’t do your homework, why you broke your promise, etc. These excuses are necessary, if you omit to explain why it happened, you will face unpleasant consequences (you will face unpleasant consequences anyway, but you can at least lower them by having a good excuse).
Then there is another type of excuse – an excuse no one is interested in. Why you scored bad on an IQ test: “126 but I got bored and quessed some of the later ones”, followed by: “oh and I had 20 min left at the end”, why you lost a tournament game (talking about go) against someone – I know a person who “has had a flu” everytime he loses against someone weaker.
As you can see, these excuses are unnecessary and they make the author seem like an… well, you choose what it seems like. 
Please, no one is interested in these excuses. You might be just lazy and/or not care about the IQ test at all. Fine, in that case you are happy with your suboptimal results. If you weren’t happy with them, you would have tried harder. (If you spotted the logical fallacy, you get one point. If you realised what I wanted to imply, you get ten points)
You might have made a blunder which cost you the game – in that case, feel free to point out that you lost the game by a blunder. But please, omit the unnecessary (and often imaginary) details about what led you to make that blunder. Or how huge advantage you maintained during the whole game (this applies even if you are a pro… being a pro doesn’t mean you can say you were winning by 30 points when in fact it was almost even and the situation was changing all the time… but sure, saying that you were winning big can improve your image and save your face (that is, if the game record is unavailable (ooops))).
And what is worst – I also make those unnecessary excuses that no one is interested in. So, while I usually don’t make any New Year’s resolutions, I will make a September the 16th resolution: no unnecessary excuses!
