you CAN predict that there will be evidence with equal probability of each direction.
More precisely the expected value of upwards and downwards updates should be the same; it’s nonetheless possible to be very confident that you’ll update in a particular direction—offset by a much larger and proportionately less likely update in the other.
For example, I have some chance of winning. lottery this year, not much lower than if I actually bought a ticket. I’m very confident that each day I’ll give somewhat lower odds (as there’s less time remaining), but being credibly informed that I’ve won would radically change the odds such that the expectation balances out.
More precisely the expected value of upwards and downwards updates should be the same; it’s nonetheless possible to be very confident that you’ll update in a particular direction—offset by a much larger and proportionately less likely update in the other.
For example, I have some chance of winning. lottery this year, not much lower than if I actually bought a ticket. I’m very confident that each day I’ll give somewhat lower odds (as there’s less time remaining), but being credibly informed that I’ve won would radically change the odds such that the expectation balances out.