Yes ur right, with 12 fails at 50%, there is a mathematical probability of only .024% to fail 12 times in a row. However, the developers do not know how to use math correctly in their calculations, and all of those percentages are fake. This goes for power boosting in any of the events. your so called "80%" boost is really like 200-250%. I could not figure out the formula they use for that boost. When I boost 20%, it goes up about 30%, when I boost 40%, it goes up about 85%, when I use 60% it goes up about 170% and when I use 80% it goes up about 250%. It makes NO sense what's so ever.
With that said, it's just they way they made this game, with no math knowledge and/or to trick players into buying more.