I am not sure if the following one counts. But it definitely opened my eyes. I heard that Latin, or rather, old French, has an influence on English. But it was not until I began to try to learn Spanish (which I think is also originated from Latin) that I realized how true it is. For instance, fast and rapid have the same meaning in English. Fast is developed from old English, but rapid is borrowed from French, and rapido (fast in Spanish) may be an circumstantial evidence. I hope I was right.