質問: The full sentence was : > > 「捨ててしまうのはもったいないと思って」 > > I think to throw away (something) is a waste > > > But why are there two て’s? Why is it not 捨てしまう?
回答: The verb is 捨てる, so its て-form is 捨てて, hence the compound form Vて+しまう becomes 捨ててしまう. If it were the casual ちゃう instead of しまう that you were using, that starts from the て-form too, but also contracts the て, so it would instead be 捨てちゃう, with just the one て. Perhaps that is where the confusion arose? Hope that helps!