When looking for evidence of an answered prayer, we only have our expectations to use as a template for how God has responded to us. But God isn't limited in the slightest by our expectations or previous experiences - He is a God of unlimited possibilities.
The people brought a blind man to Jesus and begged Him to touch the man. Maybe they were thinking of the woman who was healed simply by touching His cloak (Mark 5:25-34). They had a template. But Jesus had a different plan for this man. Taking him by the hand and leading him away from the crowd, Jesus spat in the man's eyes! Well, that's a new one! Jesus then put His hands on the man and asked if he saw anything. The blind man's vision had been restored but was blurred - he certainly didn't expect Jesus to spit in his eyes. However, Jesus put his hands on the man's eyes again - now he saw clearly.
When God does what we expect in our lives we often don't see it because it's... unexpected, sometimes invisible to us because our eyes are focused elsewhere, and we miss it entirely. Only by "blind faith" can we see God working in our lives. Read, study His Word, and see clearly how it is manifested in your own life. Believe God's Word and you'll soon see the invisible.