It's my Birthday today, but still got time to give a little love to you STM'ers 
If you're in profit and you have traction, focus on testing a new campaign and leave that one well alone!
I've never realised this was something that could kill a camp. Thanks a lot for the tip!
True, over-optimization can kill a campaign, several network favor high spenders and the real goal of every network is to sell every placement they have available ... so it would make sense for them to benefit buyers that do not optimize much. I'm not sure whether it's really the case with some (many) networks but I have seen the scenario myself too - killing too many bad placements also killed the whole campaign. Then again, I had many profitable whitelist campaigns ... as always, it's not just black&white 
Thanks for the tip dazed1!