30% probability might be around the point where we start to call things ludicrous. If you talk seriously about things that you think have a 10% chance of happening, you will be beyond the point where most people call it ludicrous, or even crazy; they simply will not understand or believe that that's what you mean.
This comment provides more confirmation for a view I've held for a long time, and which was particularly reinforced by some of the reactions to (the first version of) my Amanda Knox post.
People have trouble distinguishing appropriately among degrees of improbability. This generalizes both underconfidence and overconfidence, and is part of what I regard as a cluster of related errors, including underestimating the size of hypothesis space and failing to judge the strength of evidence properly. (These problems are the reason that judicial systems can't trust...
I would like to propose this as a thread for people to write in their predictions for the next year and the next decade, when practical with probabilities attached. I'll probably make some in the comments.