Dumbest newbie thing,you did at the drag strip.....

I had a pretty good rep on the street back in the mid 70's and alot of local guys would bring their stuff to me for mods, mainly bolt on's, cams, a few head swaps and tuning. Only caveat was i had to baseline it first and run it again after the mods. Cool thing was i got to run alot of other cars besides my own....lol. So i did a intake swap and tune for a guy going from a dual plane to a single. Went to the track and it ran 13.40/13.45. Went two rounds that day. After the swap and tune, about two weeks later, i decided to take it out. Well our local track always opened early afternoon Sat. and ran into the night, but this day was some special deal and opened early so i arrived after time trials and only about 30min before eliminations. So i guessed at a dial in at 13.15. A bud from the track came to talk to me and he was wearing a bright orange t-shirt. Then it hit me, and i took him down to the fence about half track and said if the other car redlights lean over the fence and wave your arms so i can run it out the back door and basically get a time run for the next round dial.......Brilliant plan on my part right. Well, i leave, hit 2nd gear, and look for him and what do you know, he's hanging over waving like crazy. So what do i do when i see him......back right out of it and waste the whole plan with a 15 something. So the 2nd round comes and i keep the 13.15 dial and get pushed out on the brakes with a 13.09. No doubt i left late enough to get pushed out, but it still sucked.