Our Fighter is an all-or-nothing kind of chap. When he is sure of a hit with his Greatsword he will use as much of a bonus from Power Attack as he can, ably felling some enemies with a single blow. When he is facing something a bit more difficult to hit he eschews Power Attack completely. The last fight with the Sahaugin is no exception.
There is one of the aquatic creatures left to defeat, and the others that we had killed in the fight showed them not to be too difficult to injure with a good swing of a weapon. Confidence brims in the Fighter once more, and he flexes his muscles to put everything he can in to his attack, reducing the finesse of the strike as much as possible in favour of hitting hard through the use of Power Attack.
The die skitters across the table, and it lands on a 20! Our heads spin as we try to imagine a number high enough that could represent the damage about to be inflicted by a power-critical. Except the die had landed slightly on the base of one of the miniatures; indeed, that of the Sahaugin, thwarting the Fighter's attack in an out-of-character way. The cocked die was picked up and re-rolled. No natural 20 this time, and the attack bonuses and penalties are applied until the final to-hit roll is calculated.
The result is one less than was required to hit. The Tao of Power Attack does not lie.