Some people get more of an adrenaline response when under pressure. This can be trained away, by practicing higher pressure shots until they stop becoming "high pressure", but you have to KNOW that is what you have to do to get past it. Adrenaline has a generally negative effect on fine muscle control. Players who solely focus on the tough shots in their practice both train this adrenaline response away, and improve the fundamentals applied on these specific shots.
A way to determine your adrenaline response is how much of a heart rate increase you get when on the road, not paying attention, and you drift towards the center line when another car is coming. If you immediately get a very strong heart rate spike, this is an adrenaline dump, and shows you are prone to this.
I have thought for a long time that some players are simply born with a very low adrenaline response to dangerous situations, and as such, are less prone to feel pressure. You can see the result it has on their game, as they just pop balls in at angles where the pocket "closes up". They simply don't have as much fear about shooting into a narrow pocket. Albin Ouschan strikes me as one of these type players, as he tends to have an extremely flat emotional response, even to mishit shots. Same with SVB. Both use intelligent shot design and "pool smarts" to moderate the tendency to just shoot at balls. This is a requirement to achieve very high levels. We all know folks who have absolutely no fear, but not the smarts/discipline to "lock in the win". Tony Chohan is an example, IMHO. When he moderates the tendency to shoot at absolutely anything and everything, he wins a lot more consistently.