After 40+ years smoking, I was able to quit immediately with 18mg nic, so stayed with that for 5 months or so. I began to think about cutting the nic back, but was not comfortable knowing what nic level I was using at a particular time. Just the probability of knowing I was using 12 instead of 18 would make me think I needed more. So I talked to my wife about getting juice at both levels, but having her filling a tank with the level of her choice so I wouldn't know and there would be no influence to how it made me feel.
But, and there is usually a but, I never got to that point. I got an Atlantis and Subtank and immediately lowered my nic level to 6mg and have been going fine with that since (although some might say I am hitting it a bit hard).. For now, I am fine with where I am at, but should I feel the need to drop down further, I still plan on implementing my "don't ask, don't tell" plan so I can avoid that placebo effect.