to careen wildly between two extremes, usually implying out-of-control activity due to narrow focus on some other objective, as in “They tripled the advertising budget last quarter but after the earnings miss they want to zero it out, Marketing is just going guardrail to guardrail”; evokes the image of a driver speeding down a highway and narrowly missing crashing into the protective barriers on both edges of the road; can also be used to describe reckless or unthinking behavior without connoting a binary constraint; in rare instances may be used as an adjectival phrase, as in “Tom’s strategic vision is all over the place, his thinking is just guardrail to guardrail”