Who can paraphrase this sentence for me?

My initial resolution to keep a daily gratitude list that would change my life
backfired in the best possible way. Instead of it making me happy, I use it as a wonderful tool to remind me to notice the beauty all around me.

What does the word "backfired" mean here?
BYW, here is the context relating the veru beginning of the author's gratitude list. I planned to write down three things a day that expressed my appreciation and love for the people and things around me. What began as a simple mission failed miserably by the end of January. Some days, I could not come up with one single thing for which to be grateful. On other days, I resented what my life withheld from me, instead of acknowledging the good already in it. What started as a positive exercise turned into a mental list of countless complaints and worries. Temporary family concerns and financial woes had turned me into an ungrateful sourpuss.