if there's a big discrepancy between the prediction and the true answer we can tell the network hey you made a big mistake right so this is a big error it's a big loss and you should try and fix your answer to move closer towards the true answer which it should be okay now you can imagine if you don't have just one student but now you have many students the total loss let's call it here the empirical risk or the objective function it has many different names it's just the the average of all of those individual losses so the