Stutter variance is quite the thing, yes. It'll vary depending on context - your situation, the people, the topic, your mood, how much you've slept... all factors in. All people have "social masking" to a greater or lesser extent, and this figures in stutter as well. An extreme version of this would be acting, or even singing... but there's nothing automatic about these things. The best we can do is try not to get too surprised when it happens. :)