Yeah, that's something I've been mulling - there's probably a mean between positive and negative outcomes. I must be a cynic because I'd read 'it may happen' (+ outcome) as, say, 30% but (- outcome) as 40%.
Which, given I've written 35% for the phrase originally, makes some kind of sense, and indeed expresses my mean. (although, I'm thinking maybe a 1/3 chance instead - 33.333rec%).