SwingsitlikeHogan
Major Champion
The player can declare an unplayable anywhere he likes, without giving and reason of justification, and he would be a fool not to do so if it is in his advantage. Sometimes the rules of golf are arbitrary and a bit stupid. Occasionally, they give you a good break. If so, grab it and remember it next time the more usual bad break happens.
Like when you miss a short putt on a wickedly sloping green and your ball ends up in a greenside bunker right against the face. Just declare it unplayable and replace it from whence it came - back on the green - and add a shot - as as you now know the putt you should be better placed to hole it.