Why does beginning have a double n and happening only have one?

The difference in spelling between "beginning" and "happening" is due to the rules of English morphology and etymology. The Word "beginning" is derived from the Old English Word "beginnan," which had a double "n" in its root form. On the other hand, "happening" is derived from the Old English Word "happen," which only had a single "n" in its root form. The variation in spelling reflects the historical development and evolution of these Words in the English language.