Over the years NASCAR has installed a lot of rules. Those rules are created for safety and to provide stiffer competition.
The "lucky dog" rule was put into effect to minimize the danger of racing to the yellow flag and lining up a bunch of lapped cars next to the leaders, causing slowdown.
The rule is also there to promote competition. A driver who is a lap down is not always someone who should be a lap down.
There are times when a driver is very fast and something unexpected, but not the race ending, causes them to pit and lose a lap. Or a driver that has been slow finds the right combination on his car but he's a lap down due to his earlier lack of speed.
So, the lucky dog is designed to give the fastest driver, who is a lap down, a chance to compete for the win again, hopefully due to hard work, clever pit strategy, and a fast car.
This isn't how it happened at Darlington.
Martin Truex Jr. was very fast all day. He was running in the top five when there was a caution around lap 240. On the restart his transmission locked up, halting his ability to shift.
In the pits the crew cleared the jam and got Truex back onto the track, barely behind the pace car but a lap down. For the remainder of the race Truex ran in the top 10 physically, but, still, a lap down.
His car was fast enough to be in the top 10, but, due to long stretches of green flag racing, when the cautions did come the leaders were in the process of lapping other cars.
This meant that the car that was just lapped, that obviously was not fast enough to run with the top 10, was given the lucky dog. Truex finished in 19th place, the first car a lap down. His position is in no way indicative of the way his car, his team, or he himself performed.
The lucky dog gives those drivers and teams that are a lap down something to fight for, but let's reward excellence instead of sub par performance. Maybe the lucky dog should go to the car with the fastest average lap speed of the last five laps, that way it's always earned.
My opinion may be biased in this instance because he is my favorite driver, but I think everyone is losing out when competitive cars can't race with their equals.