Even if the conditions are such that if you don't meet the 30% chance for victory, you are guaranteed to finish last, since there is absolutely no risk involved (being a casual game), there is absolutely no legitimate reason to not try for the win. If this were a situation with actual bonuses tied to any of the various finishing positions (ie, winner gets promoted, loser gets fired), then my answer might change. But a risk/reward analysis of a situation with no repercussions whatsoever is unnecessary. Just go for it and see what happens.