Knowledge and experience are two different things. If you've ever been told not to do something for a specific reason, that's knowledge. If you've gone and done it anyway, that's experience. Last year, my son was sitting on the counter at my parents house watching my mother cook. Although we've told him countless times, "Don't touch the stove because it will burn you", he learned how right we were when he wasn't thinking and accidentally placed his hand on the eye of the stove to prop himself up. Will's knowledge turned to experience in a split second.
Jesus was trying to get this into the heads of the disciples in Mark 8. He had just healed a mute man and a deaf man, not to mention having just fed 4,000 people. Jesus and his disciples had climbed into the boat when in verse 14, we pick up the story. "The disciples had forgotten to bring bread, except for one loaf they had with them. 'Be careful,' Jesus warned them. 'Watch out for the yeast of the Pharisees and that of Herod.'" The disciples were confused and thought Jesus was chastising them for not bringing the extra bread leftover from feeding the masses. Verse 17 says, "Aware of their discussion, Jesus asked them: 'Why are you talking about having no bread?: Do you still not see or understand? Are you hearts hardened? Do you have eyes but fail to see, and ears but fail to hear? And don't you remember? When I broke the five loaves for the five thousand, how many basketfuls of pieces did you pick up?'" The disciples said twelve. Verse 20, "'And when I broke the seven loaves for the four thousand, how many basketfuls of pieces did you pick up?' They answered, 'Seven'. Jesus said to them, 'Do you still not understand?'"
Why was Jesus referring to the Pharisees and Herod as yeast? If you've ever made bread before, you know a little bit of yeast can work its way through a whole batch of dough. Sin operates in the same way and it could be a variety of sins like faithlessness, haughty attitude, fear, hate...you name it. Sin keeps us from an intimate relationship with God.
I can just imagine Jesus was about ready to pull his hair out. Allow me to give a Barbie translation to this: "You mean you've seen me (Jesus) provide so many times before and deal with whatever is going wrong and you still don't get it? What's wrong with you people?"
God has provided for you countless times before, even when you didn't think you could handle another minute of it. Just as he did miracles for the deaf, mute and hungry, Jesus has enough because He IS enough! Stop relying on your knowledge and remember your past experience with Him!