The Prophet, peace be upon him, had given dawa to 26 tribes before going to Medina. Why did he not give up after the first few rejections? Why not after being beaten in Ta-if? He kept going because He knew Allah would never abandon Him. This attitude is from the inward sunnahs of the Prophet, peace be upon him. It is so essential that had it not been there we would not be here.
Have a good opinion of Allah.