When beliefs and experiences don't match, we become confused, frustrated, and disappointed. This is why positive thinking is so limited. It often seems forced or inauthentic and it only works when we have the experiences we desire.
The problem with positive thinking or affirmations is that they operate at the surface level of conscious thinking and do nothing to contend with the subconscious mind where limiting beliefs really live.
The next day as they were leaving Bethany, Jesus was hungry. Seeing in the distance a fig tree in leaf, he went to find out if it had any fruit. When he reached it, he found nothing but leaves, because it was not the season for figs. Then he said to the tree, “May no one ever eat fruit from you again.” And his disciples heard him say it.
— Mark 11:12-14
Now in the morning, as they passed by, they saw the fig tree dried up from the roots. And Peter, remembering, said to Him, “Rabbi, look! The fig tree which You cursed has withered away.” So Jesus answered and said to them, “Have faith in God. For assuredly, I say to you, whoever says to this mountain, ‘Be removed and be cast into the sea,’ and does not doubt in his heart, but believes that those things he says will be done, he will have whatever he says. Therefore I say to you, whatever things you ask when you pray, believe that you receive them, and you will have them.
— Mark 11:20-26