Traditional Idiom & Slang can t make heads or tails of something Keener : I m not sure now if I want to marry Gloria or not. I still love Lisa. Slacker : Really. What are you going to do? Keener : I don t know who I want to marry. I can t make heads or tails of it. Think of a coin. A coin has two sides; a heads and a tails side. When you simply cannot make a decision, you say I can t make heads or tails of it. This means that even if you flip a coin to let the coin help you decide, you still can t come to a conclusion.