CoupeBoy speaks from past experience, if I had to put a percentage on the number of times that I've put in a distributor the right way, I'd say it would be something like 15%. When I put the motor back into the wife's pickup in October I put it in 180°, then I watched my step-brother stare at me in disbelief as I swapped the plug wires. 2 minutes later bingo, it fired right up!
All the freaking time, and when I think it's right I correct it, and magically it would have been right the first time, but I second guessed myself. And yes I do know that there is a process for figuring out when the number 1 cylinder is coming up on pressure and by watching the rocker arm, but that takes me more time then doing it twice.
-ron