I was reading this speech from Andy Grove, Intel chairman, from 1998 and while the whole thing is a bit hard to read, this bit about strategic inflection points and competition was quite interesting:
Some key warning signs that hint that the change you are dealing with make a Strategic Inflection Point is when it is clear to you that all of a sudden the company or the entity that you worry about has shifted. You have dealt with one particular company or establishment as a competitor all your life and all of a sudden you don’t care about them, you care about what somebody else thinks. I have this mental silver bullet test. If you had one bullet, who would you shoot with it? If you change the direction of the gun, that is one of the signals that you may be dealing with something more than an ordinary shift in the competitive landscape.