Being a missionary is a job of constantly learning, constantly evaluating what you thought you knew, and looking at things in a new light, or at least a new frame of reference. If you stop learning, you stop being effective.
People ask us why we're attempting to translate the whole Bible and not just the New Testament. When we were young missionaries in training, we thought, "Hey, PNG has the whole Bible in the trade language, so we only need to translate the New Testament into the heart language." We have since needed to repent of that.