Even "simple" can be confusing. Last week I encountered a Petrol pump with A,B, C options (let's call them Unleaded, Plus and Premium). They only had A (Unleaded), so they put a paper sign on the panel, above the two other buttons saying "Unleaded Only".
What happens? People only try to press B or C (Plus and Premium), thinking there's no Unleaded,
I pointed out to the attendant that they should put their paper sign OVER the two buttons to physically hide them. I get some response about how they did that, but the rain messed up the ink. BS, it hasn't rained for five days at that point. [Yes, this is the great 2017 Texas Not-A-Gasoline-Shortage]