Hmmm, actually what can be external but not internal? Sure, the main cause may be external, like what I encountered in my last tournament, but in the end the feeling is processed internally. And is not some anxiety, but disgust, or other dissatisfaction
Yep, I vote for that. This happened to me. I used to discover a lot of things, on my own, or in books, and then try to apply them in games. And at one level, nobody will fall for a snapback for example. So, suddenly, or maybe building it up and bursting, the lack of novelty made me quit. The novelty of participating in a huge event with thousands of participants made me come back for a last tournament though.
Yep, not actual fear, just a feeling or certainty. I remember the feeling decades ago of waiting for the opponent to make a move and see if the trap worked. Maaan better than sex, since the tachycardias lasted longer. Also freshly married my wife insisted me to come to sleep, but Go or many other things kept me at my computer. So how to call it now when I am in mood of wasting time with a hand of solitaire instead of a game of Go?
But sure the factor of wasting time is a big factor (based on the perception of doing something interesting) It happened that this last tournament I touched somehow this issue. Is a correspondence tournament, so everybody decides for how much time spends in the games. But the span of the tournament on which is spread your own allotted time is decided by some other factors. And some casual comment of mine stirred a pot of wasps. Damn, there are some pressure that built up. Many, (or maybe only few, but it looks like many) even decided to quit the tournament.
So definitely the feeling of wasting time is a factor that weigh a lot, a lot more than any fear in the decision of quitting Go.