Education
Apurva feels impressed because for complex tasks like image classification, "simple" things like linear regression is sometimes good enough. Alex and Edderic warn listeners to basically allocate more time to this lesson, because there's a lot of hard reading. Edderic confesses that he failed to implement the backpropagation algorithm in the machine learning course he took during college, and promises to himself that he would get salvation by implementing it correctly this time. Image is taken from Michael Nielsen's Neural Networks and Deep Learning book (http://neuralnetworksanddeeplearning.com/chap2.html)