The tech tree for me was very confusing when I first started out. In all the games I've played, availability of items in the tech tree are not based on chance. You upgrade to item 1A so you can get item 2A and then get item 3A. In elemental you upgrade to item 1A and item 1B may not be available 90% of the time, so you are forced to choose item 2B instead and hope that the next time around item 2A will be available. Confusing.

I think there needs to be some sort of visual indicator on the breakthrough window that shows all the breakthroughs which would have been possible as well as which ones are available.