What does Matthew 16:9 mean?

Jesus asks the disciples a question which could easily be translated as "don't you get it, yet?" They have been so preoccupied with food that when Jesus warned them about false teaching, they decided He must be upset about their failure to pack bread. In response, Jesus called them men of little faith. His concern is that they're distracted by something which their own experience clearly says is no big deal. He recently rebuked critics for ignoring miracles when they questioned Him (Matthew 16:1–4). The disciples aren't being stubborn, but their distraction is also based in forgetting what they've already seen.

And so, Christ reminds them of events they were present for. These men saw Him feed five thousand men, plus women and children, from just five loaves of bread. Matthew records this event in Matthew 14:13–21. It had taken place recently. Jesus had told the disciples to feed the crowd. Their response had been that they had only a tiny amount of food. From those meager supplies, Jesus distributed to the disciples enough bread for all those thousands of people. He reminds them now of the twelve baskets of leftovers they gathered up after every person had eaten his or her fill.

The implication is crystal clear. Why would the disciples be worrying about bread when they have seen Him feed thousands in this way? More importantly, why would anxiety about bread override understanding what He was trying to teach them right now about the Pharisees and Sadducees (Matthew 16:5–8)?