Isn’t a saving throw because your physically or mentally trying to resist an effect?

@JeremyECrawford Isn't a saving throw because your physically or mentally trying to resist an effect? If so why no rule to choose to fail?

— Steven Connor (@Mazoshi1987) October 25, 2016

Effects that involve saves are intended for you to use on others. If you use one on yourself, you're in DM-adjudication territory. #DnD https://t.co/0K5XAPTCIz

— Jeremy Crawford (@JeremyECrawford) October 25, 2016