It has been determined that impulse control has a positive correlation to intelligence and greater life success. I can see that, since popping off about your boss being a dick at the Christmas party would a) not be too wise, and b) land you on the street without a job. Hey, that’s a hypothetical, but people have done dumber things!
So, are shy folks and introverted folks lack of yapping off the top of their heads randomly a cause of better impulse control or a crucial characteristic of it? Well, from what I know of introverts, being one myself, they hold back because they’re thinkers who can appreciate the dire consequences of speaking out of turn. We have a tougher time recovering from the fallout with our maddening propensity for rumination.
When you have a filter as strong and tightly knit as an introvert's, it's easy to not make a damn fool out of yourself on April 1st or any other time.
So, I’ll put the question out there: Have you ever said the absolutely wrong thing in a social situation? Something like accusing someone of being so stupid they rode the little yellow bus to attend school when they actually did ride the little yellow bus? This is a true and unfortunate example from my own life-- a former co-worker said this to someone in front of a crowd of people. No, my co-worker was not an introvert. Go figure, but we’re not perfect either. Everybody plays the fool sometime after all.