Have To (-아/어야 돼요)

돼요 comes from 되다, “to become” or “to be okay.” -아/어야 돼요 literally reads as “it only becomes okay if…”, which is exactly why the construction implies obligation. You’ll also hear -아/어야 해요, built on 하다 instead, meaning almost exactly the same thing.

감기에 걸리다 (“to catch a cold,” literally “to get caught by a cold”) is worth learning as one fixed chunk rather than building it word by word. A surprising number of illness expressions in Korean work this way, describing symptoms as things that happen to you rather than states you’re simply in.