One problem I see with self-affirmations is that they only change your perception of what you can achieve, not what you actually can achieve. No amount of self-affirmation will help you become a painter unless you take the pain of learning how to paint. And failed expectations after some time build frustration. So you must be cautious of what you make yourself believe.
There is a joke about a guy that was praying his whole life asking god to let him win a lottery. He never did, and after his death he asked god why. The god answered "What could I do? You never bought a lottery ticket".
Nobody said you shall spend your life before a mirror, saying affirmations instead of living your life. They are a way to rewire your brain for assumptions you want to get rid of, and break bad habits without needing a therapist. Acting is crucial. People who don't act are stuck and/or depressive, and they may use affirmations to pretend to feel better. But that's just a way of using a tool the wrong way.
Affirmations also should not create expectations in you. They change the way you perceive the world, and yourself. If someone creates expectations of feeling better after saying affirmations (and then is disappointed), then that's a problem of its own - it just means that you used it as a quick fix instead of trying to change your beliefs and assumptions.
I think that self-affirmation makes sense as a counter to whatever is being pushed upon you. It's easy to get caught up in the minutae of daily BS at your job, and end up in a rut, thinking that something is wrong with you.
I worked at a place where organizationally, we just failing. It's depressing working for a sinking ship, and as a crewman on the ship, you can feel like your bear some responsibility.
Self-affirmations certainly can't be a replacement for all work... BUT, it is well documented that those who have an optimistic mindset will persevere more in the work that they do and overall have better outcomes.
