I can take this topic one step further too and attempt to illuminate part of why we have come to believe in illusions like choking and being clutch. Basically, for me it seems like this is what's really going on:
Success and failure during high-pressure situations is an effect. We tend to need to define a cause for it and generally, this cause is defined with an attribution error through calling it "clutch" or "choking". In reality, it's really a product of the same teamwork, education, and ultimately, skills that can increase chances of success in all aspects of a game. If you disagree with this and/or want to understand the reasons I suspect this, then, please, keep reading.
First, we'll need to understand what an attribution error is and that we, human beings in general, have a profound tendency to need reasons for everything (this perhaps stems from our general discomfort with uncertainty). Basically, an attribution error occurs whenever we come up with a reason for why something happened and that reason is inaccurate.
Social psychology defines this specifically as a tendency for people to associate what someone thinks or does to part of their character rather than some other motivation compelling us to think and/or act in a certain way. For example, if someone is unaware of the amount of work a professional athlete has put in to develop his or her capabilities, fans might attribute it to "natural athleticism" over specific aspects of their training. We might think they have "drive" when during their childhood, they may have actively wanted to quit if not for certain pressures from other people that kept them practicing, playing, and learning. Michelangelo has a great line that attempts to address this tendency with "If you knew how much work went into it, you wouldn't call it genius." In his case, proclaiming genius, a character quality, is the attribution error.
In other words, we may define someone like Russel Wilson as clutch because we don't get to see or hear about many of the specifics about why he is able to succeed in certain situations, such as seeing the moments where he and other members of the offense are watching film and they get to see a tendency of a defense they can exploit, seeing that a creative-looking scramble for a big completion was really something that had been done before in practice months before, and all the other potential reasons RW and co. might better know what to do in most situations than many of their opponents.
To put it simply, we believe Russel Wilson is clutch and other players, such as Tony Romo, are chokers partly because we're fundamentally motivated to define causes for effects (even if relatively inaccurate) and this can be done quickly and simply (but not as accurately) through defining causes for people as part of their character rather than their other influences and motivations. If we really knew how much preparation went into their games, we might not call it clutch or choking.