Back on topic:
50/50 situations almost never occur in Diplomacy. There are always extra considerations you can take into account, such as what the opponent thinks is the better move, or what the opponent thinks you think is the better move, etc. If you think it is a 50/50 situation you're probably underthinking the scenario.
Take the Classic S01 situation:
French A Mar-Spa
Italian A Ven-Pie
Let's assume A Par has bounced in Bur and can't help.
This initially seems like a 50/50 scenario from France's perspective - France has the options to either move back to Mar, betting on the Italian bouncing him, or stay in Spain, betting on the Italian holding. Guessing wrong in both scenarios has the same outcome - a build denied for France and making him unable to build in Marseilles - and guessing right also has the same outcome, as both would give him a build and enable him to build in the south.
From the Italian's perspective, it is not necessarily 50/50. Italy can choose to either move to Marseilles, betting on the Frenchman leaving it open, or hold, betting on France moving back. However, the outcomes are not the same this time. If Italy guesses right in the first scenario, he gains a build, but also has started a war with France. If he guesses right in the second, he doesn't gain anything but denies France the build, and, although he probably has a very annoyed France on his hands, hasn't started a war. With wrong guessing, he starts a war and doesn't gain anything in the first scenario, and still doesn't gain anything but doesn't start a war in the second.
What the Italian thinks is best will vary from game to game based on the situation. If he has a very strong ally in England and a neutral Germany, he may not care about starting a war as he knows France will not be able to react, and so the first situation would be more appealing, as it potentially gives him a build without any disadvantages. If he doesn't have any commitment from EG, or if the East is looking to be more of an issue, he might be worried about starting a war and so the latter option would be more appealing, as it would potentially weaken his neighbour, so meaning he wouldn't have to worry about his western front so much, without risking a war.
The fact that the better option for Italy changes depending on the situation means that, even though it looks like it's a 50/50 guessing game for France, he can work out what the better option is for him by examining the board to see what Italy would think it is better to do, and then entering orders to counter that. Therefore, it would not be a 50/50 situation anymore - it would be weighted in favour of countering whatever Italy thinks it is best for him to do.
Of course, you then go down the avenue of Italy trying to counter this by thinking as France would, and then it gets complicated, but it still wouldn't be 50/50. A lot of what seems like decisions that would have to be based on chance in Diplomacy can be based on your skill instead if you think about it in-depth.