"Yet even now, says the Lord, return to me with your whole heart, with fasting, and weeping, and mourning." (Joel 2:12)
"At the time, all discipline seems a cause not for joy, but for pain, yet later it brings the peaceful fruit of righteousness to those who are trained by it." (Heb. 12:11)
God never tells a lie. If he promises something, he will do it. He is totally, completely trustworthy. Satan, on the other hand, will do anything to get you to turn from God, including lying to your face. For instance, in the garden Satan tells Eve that if she will eat the fruit she will be like God. The lie is (a very subtle one) that she is already made in God's likeness and image. St. Ignatius says things like desolation and discouragement come from trusting the lies of the devil more than the truths and promises of God. Discouragement is never from God because it weakens faith and hope.
Moses said, "Okay, Lord, I've got them in the desert. What's the plan?" God's answer--"Trust in my presence." When Jesus appears to Paul on the road to Damascus he doesn't tell him of all the plans he has in store for him. He only tells him to go to the city and wait to be told what to do next. When God tells us to do something we need to do it, not ask about the payoff or the long view. This starts with things like the ten commandments, but, as St. Ignatius points out, continues with particular movements of the heart that we can discern by the rules of desolation and consolation (under the wise direction of a spiritual guide).