As for affirmations, I suspect you would have to ask a "street-wise" successful sales manager, not an "ivory tower" marketing manager. I once watched a weekend regional meeting of managers of a shoe store franchise. They received not merely factual information about sales in the coming year, but went into "rah rah mode," complete with a multi-media rousing football theme presentation. I thought: This is not something grown men in prim business suits would ever do... unless it measurably affected the "bottom line" of the accounts ledger.
As for me, I don't have to ask anyone because I have tried affirmations for myself. But not recently. I haven't done so for years now because of, er, - My-life-is-improved-enough-already, thank you.
For me, affirmations worked. I am sure an outside observer would have noticed changes in my behavior which means, therefore, I changed my life... not just my thinking.
What doesn't work, in my opinion, is merely saying a slogan once or twice every morning. Better to make a "concerted effort." For me this effort meant affirming several times per day, using all my senses, by writing, reading, and saying aloud. And using repetition. I seem to recall Abraham Lincoln doing something similar. He answered his law partner once that the reason he read aloud was to, in effect, "get stuff to stick in."
Happy new year.