Black Knight Syndrome (BKS) is the condition of being pathologically unable to acknowledge defeat.
The syndrome takes its name from the Black Knight in Monty Python's 'Holy Grail'. In this motion picture the Black Knight loses an arm in a sword fight with King Arthur, and claims that "'Tis but a scratch". On losing his second arm the Black Knight says that it is "Just a flesh wound". After losing one of his legs the Knight exclaims "I'm invincible!", and when his second leg is cut from under him he says "All right; we'll call it a draw".
BKS is commonly found in people afflicted with the Dunning-Kruger Effect, and it is typified by people who refuse to accept evidence that demonstrates beyond doubt that evolution is a fact, or that global warming is real, or that HIV causes AIDS. Indeed, such people have an irrational inability to accept the truth of any of a number of other scientific disciplines where the physical evidence trumps their conspiracy theories, vested interests, and/or ideologies.
BKS is also frequently found in people otherwise prone to Denial Silence
The typical pattern of a conversation with a BKS afflictee involves the opposing, educated party presenting supportable fact after fact, carefully referenced and explained, whilst the ignorant BKS sufferer simply contradicts each devastating point with random, unevidenced counterclaims of his or her own. Due to this strategy, such exchanges rarely have a satisfactory conclusion.
In an online debate about the reality of modern global temperature increase, Vincent was insistent that no warming had occurred over the 20th century, no matter how much independent evidence was presented to him, from many countries and employing many different lines of analysis.
The thread would have persisted for months, if not years, had not the other blog participants acknowledged that Vincent was exhibiting a severe case of Black Knight Syndrome, and subsequently quarantined Vincent to a rubbish thread.