어야 알다

you won't know till you try

-어야 means "only if, not until", so this says knowing is impossible before the action happens: 가봐야 알지 "we'll only know once we get there", 먹어봐야 알겠네요 "you'd have to taste it to know". Half these lines use it exactly that way, as a polite refusal to guess about something still ahead. The verb in front is very often -어 보다 "try doing", giving 해 봐야 알다, "you have to try it to find out".

Register: casual spoken