That's one of the reasons why I give "thanks" and always add the caveat, "I give thanks for this, or something better, for the highest good of all concerned" even if that might mean the "something better" is not at all what I envisioned. It's my way of turning it over to the Cosmic's/God's/Great Spirit's will, not mine.

I am not sure it's entirely the fault of the people who are teaching it; in a couple of personal friends' experiences, I think their misinterpretation really messed them up, i.e. thinking one can sit around and do nothing but affirmations is supposed to magically manifest whatever they need or want. It doesn't work that way.

It does, however, as you noted, help if we have a positive outlook on life. There've been plenty of studies which show successful people "appear" to be successful before they became that way, because of the way they dress, speak, look like, etc. always being positive in what they project. That helps to draw success to them, imo.