Potential fields: simple forces, a real weakness
The potential field method treats navigation like physics. The goal exerts a virtual attractive force that pulls the robot toward it, and every nearby obstacle exerts a virtual repulsive force that pushes the robot away, stronger the closer the obstacle is. At each instant, the robot just sums up all these forces and moves in the direction of the combined result. It's simple to implement and cheap to compute, which made it popular for exactly the reason this course cares about, speed.
But potential fields have a well known failure mode called local minima. If the attractive pull toward the goal and the repulsive pushes from obstacles happen to cancel out, the robot ends up with zero net force and simply stops, even though a clear path to the goal exists. The classic example is a U-shaped or C-shaped wall between the robot and the goal. The repulsive forces from the walls on either side push the robot back toward the center exactly as hard as the goal pulls it forward, and the robot gets stuck oscillating or standing still in the mouth of the U, unable to figure out that walking around the wall would work.