Isaiah: From what I understand, God instructed Isaiah to go and speak to the people however informed him they were not going to hear nor understand him (Isaiah 6:8-13)... for God had "blinded their eyes and hardened their heart[s]" (John 12:40) for an undisclosed period of time. How easy would it have been for Isaiah to say, "Well, then, what is the point of me going to chat with them? Why go through the hassle?"
Ananias: After God had struck Saul of Tarsus with physical blindness (to match his spiritual blindness) God put it on Ananias's heart to seek Saul and restore his vision. Now, I am certain Saul's reputation preceded him and I would not have blamed Ananias if he had said, "WHAT! You want me to go meet up with this murderer of Christians and heal his eyes? For what purpose? What will that accomplish?"
Moses: Moses was up against a powerful and hardhearted man who was not about to listen to anything God had to say. How frustrating would that have been to return day after day to ask time and again for the release of God's people? Not even plagues were working until God had to use extreme force and take Pharaoh's son.
God nor Christ Jesus ever said being a follower of Christ would be easy. In fact, I do believe He stated quite the opposite. So, I preach to myself two things during tribulation and a lack of desire to press on:
#1. If God has placed something on my plate then obviously I can manage it because God never gives a person more than they can handle. #2. God's grace is sufficient.
But he said to me, "My grace is sufficient for you, for my power is made perfect in weakness." Therefore I will boast all the more gladly of my weaknesses, so that the power of Christ may rest upon me. (2 Corinthians 12:9. ESV.)