...because the quotes are getting so long, i'll start anew.
I absolutely have to agree with drza44. 99% of the time, "clutchness" is one of 2 things: either heavily heavily circumstance and situation dependent (selection/sample size bias, as in players on teams that happen to make it far due to the entire team makeup have more chances at important clutch moments than those stuck on irrelevant teams) or heavily heavily confirmation biased: the narrative about player X is that he's clutch, so any instant of "clutchness" confirms the preconceived notion while any incidents that refute the notion get quickly forgotten. This also happens vice versa, where a player is determined to be "unclutch," and all evidence to that point is kept in the public consciousness while contrary evidence is thrown out.
Essentially, people, but ESPECIALLY media personalities, construct their sports experience through a narrative, and most people don't like that narrative to change. This is what is responsible both for inaccurate reputations as well as drastic swings in opinions. Example 1: Kobe is extremely clutch. Every highlight buzzer beater he makes is held up as proof of this fact. Yet any stats show that, in crunchtime, if the ball is in the air and you bet he misses everytime, guess what, you come out ahead. There have been other players more clutch than Bryant. However, he has two benefits: 1) playing next to Shaq during his early years when his narrative was being constructed, and 2) having had that narrative constructed early, the parts that support said narrative receive disproportionate attention than those that refute the narrative. Example 2: KG. One of the greatest players of all time, stuck on a terrible team with a terrible GM that lost the aid of any first round pick for 5 years. Put him next to Shaq from 1995-2004, see what happens: a very, very different narrative. He undoubtedly becomes a key player on a team that wins several titles, as he and Shaq complement each other perfectly with inside-outside from the 4/5 spots on both offense and defense...seriously, who scores against a frontline of young Shaq and young KG? He even gets a "clutch" rep as he puts up his near triple double numbers in a few winning game sevens rather than losing game sevens due to an atrocious supporting cast. From then on, any time he has a big moment, this is then further proof of his greatness and his failures are brushed under the rug, instead of having failures blown up as proof of collapse and successes swept aside.