I am profoundly confused by these two roots. Why should I not kredi someone who is not fidinda, why do people fidas in God, but things are nekredeblaj? What question should I pose in my mind when deciding which root to use in a word I'm going to say? Thank you!
Update: Turns out I was wrong about the phrase kredi je Dio, I don't know why I thought it was fidi. That certainly added needlessly to the confusion.