The art of positivity is, indeed, to pick your battles wisely! We cannot avoid negatives in a polar world of existence (biorhythms go naturally up and down, full to empty, catabolism-anabolism), but we can remember that life is not meant to be a struggle, and can become an adventure.
Self-doubt and defeatism can take a life-time to shake - or so it seems to me, still struggling daily - or not! No: adventuring daily!