policy gradients to train a neural network to play the game of pong that's amazing right well yes it is but as always there are a few very significant downsides to using this methods let's go back to pong one more time so imagine that your agent has been training for a while and it's actually doing a pretty decent job at playing the game of pong it's bouncing the ball back and forth but then at the end of the episode it makes a mistake it lets the ball through and it gets a negative penalty so the problem with policy gradients is that