the models of degree and don' seem to expect bright future for our startup they tried so hard to model the given data correctly that they are clearly useless to extrapolate further this is called overfitting on the other handthe lower-degree models do not seem to be capable of capturing the data properly this is called underfitting so let us play fair to the models of degree and above and try out how they behave if we fit them only to the data of the last week after allwe believe that the last week says more about the future than the data before the result can be seen in the following psychedelic chartwhich shows even more clearly how bad the problem of overfitting isstilljudging from the errors of the models when trained only on the data from week and afterwe should still choose the most complex one error = error = error = error = error = training and testing if only we had some data from the future that we could use to measure our models againstwe should be able to judge our model choice only on the resulting approximation error