[blueprint]

IMHO it's not actually possible for something to ever be 100% priced in, which has the surprising meaning that people need to also discuss how much of an event is priced in when they speculate whether something is or isn't priced in.

[Obi_Juan_Kenobi]

People tend to ignore the inherent risk of time when considering something 'priced in'.

If an event is set to happen in an hour, you can be fairly certain it will happen, so it should be strongly 'priced in'. If it's happening months or years out, a lot could happen in the meantime, thus it's not 'fully' priced in. It's not a discrete event, but rather some sort of curve (perhaps sigmoid?) that depends on perceived risk.

[vanattab]

Can you elaborate on your meaning?

[blueprint]

Please see my reply to eximius.

[eximius]

Why is it impossible?

[blueprint]

It can be virtually guaranteed that not everyone who might buy or sell will know about and properly understand a given event.

[eximius]

People can be correct for the wrong reasons, though. Wisdom of the crowds (and the Central Limit Theorem) would make me expect that it would be very close is most cases, with random noise being the most common distance from the truth.