Players Mistakes.

Every Darts Player will acknowledge that being able to count is an essential part of any darts game. When a player gets down to a finish the ability to work out a tidy finish on a double that they feel confident about as each dart goes in helps keep the player a little more relaxed and therefore helps them to throw just that little bit better. Some players say they respond to stress and it raises their game, but there is nothing like the stress induced in a player when they miscount. It makes most players totally confused over what they have scored and should then go for at the end of a game. It will upset the rhythm and throw of anybody. You get the same reaction when the player hits something unexpected and they stop in their tracks before having to ask the marker what is left. When told the correct score some players will sometimes recover from such mistakes, but most will miss the target. A good marker will be on the ball and will almost anticipate the players request for the score, but Markers can and do make mistakes as well under the stress of marking. (See Articles: - Stress & Mistakes and A Good Marker.) 
Normal pub players often “Lose the count,” as it is often phrased, but you don’t really expect it of the Pro’s.

Admitedly, Lee Mack, although a celebrity, is not a Pro player, but in the recent Comic Relief Darts Special Competition he miscounted on his finish of 50 hitting a 25 and then getting a one that left him double 12, but instead went for double 8 and hit double 16. Martin Adams on the other hand, Lee’s partner in the game, is a Pro darts player and he made his own unthinkable mistake in the same competition when he went for the wrong double a couple of games later going for double 8 instead of double 4 which lost him the leg. This sort of mistake can arise from some markers who score the remainder incorrectly by putting X 8, for double 8, on the board instead of 16. Markers can also cause players to go for the wrong finish with bad marking by putting the scores in different columns. For instance one marker might put the two players remainders in the two central columns and their scores in the two outer columns whereas another marker might put each players remainder to the left of their last scores. This can make a player think he is left with a certain number that was in fact his last score and not his finish. Perhaps Daryl Fitton’s mistake of “Putting one out of the board,” in the same competition was a little more forgivable as the Pros will often go for two double Tops with 80 left or two double 18’s with 72 left. However, I still feel that faced with 99 left he would have been better going 19, Treble twenty and double 10 instead of 19, tops, tops. Missing the treble twenty would probably have scored twenty and left his partner just that little bit nearer instead of scoring nothing for the dart out of the board. I know I am not a pro like Daryl, but I was always told a safe shot is always the way to go. (See; - A Word Of Warning.)

However, even a safe throw doesn’t always win the day as was the case in this years UK Coral Open (2015) when we saw 3 X Canadian World Champion John Part mistakenly put a dart out of the board when he missed a big 18 that he was going for to set up a finish in the 1st Round. His opponent, 20 year old Mike Zuydwux from the Netherlands, went on to beat him 5-2.
Games can be over so quickly that any mistakes on a darts board can cost any player the game no matter who you are, or how good you are.