<human>:  Why is backpropagation so important in neural networks?
<bot>: Backpropagation is a learning method that is used to train neural networks. It is a very effective method for training neural networks. It is used to calculate the gradient of the cost function with respect to the weights of the network. This gradient is then used to update the weights of the network. This allows the network to learn the correct weights for the task at hand.