Calling yourself a failure turns one event into an identity. Keep it an event.

There is a large difference between something failing and you being a failure, and the language slides from one to the other without permission. An event has a date, a cause, and a next attempt. An identity explains everything and suggests nothing. Once the word attaches to you rather than to what happened, no move is left.

When you catch the sentence forming, make it specific instead: this attempt did not work, for these reasons. Then name one thing you would do differently. Staying specific is not optimism, it is accuracy.