While your comment about drug tolerance rings true, I think you're indulging in logic at the cost of common sense. I know many people -- myself and my wife included -- that are "one cup a day" types. I've had just one mug of coffee every morning for most of the last 10 years.

I'm merely dispelling the "common sense" myth that caffeine has a built in limiter, thus making it "safe" without any conscious effort on your part. It doesn't and it isn't.

In a high stress startup environment that provides an unlimited amount of coffee and energy drinks and always seems to be in crunch mode, it's easy for your caffeine consumption to creep up to "could kill a horse" levels. I've seen it happen to others. I've had it happen to me. The end results aren't nearly as bad as, say, alcohol addiction, but it's still not something I want to live through twice.