Why do the words I know not mean the same in Spanish? Why can't Spanish just behave?

Many pairs of languages have false friends. That is, words that share a common origin or that are loanwords from one language to another, but that changed their meaning in the process. Like how the word “sake” that refers to any alcoholic drink in Japanese is used in English to refer specifically to Japanese rice wine. Or how “diverso” in Italian is used with the meaning of “different”. There’s no more reason for other languages to adapt to the way English works than there is for English to adapt to the way other languages work. Each language evolved in its own way and there’s no way around getting used to the way that native speakers use the words in their language. To avoid having problems when learning false friends, we recommend not making assumptions about the words that you encounter. When listening to or reading the language you are learning, let the context dictate what the words can mean, and don’t try to impose your own meaning on sentences based on what you believe you know about the words.