I don't know what it was, but in some of the fights you could tell who was scared and who wasn't. In the first fight against Ruddock Mike, allegedly, looked at Razor during the stare-down and told him "You know I'm going to kill you right?," to which the taller fighter responded "I know".
What? I didn't get that at all! Ruddock looked very willing to take on Tyson. Tyson had already lost to Douglas and his "aura" of invincibility was shattered. Ruddock lasted a lot longer than most of Tyson's opponents and the fight was stopped in the 7th round. A stoppage that most felt was premature.
To say that Ruddock went into that fight "knowing" that he will "get killed" is simply not true. If it was as obvious as you claim it was why hasn't anybody else, any commentators and experts, make that same observation?