clearlythe combination of these two lines seems to be much better fit to the data than anything we have modeled before but stillthe combined error is higher than the higher-order polynomials can we trust the error at the endasked differentlywhy do we trust the straight line fitted only at the last week of our data more than any of the more complex modelsit is because we assume that it will capture future data better if we plot the models into the futurewe see how right we are ( = is again our initially straight line