Elsewhere I write

If you practise Buddhism, doing traditional meditations and, separately, thinking about what you learn from them, the thing that stands out is the craptastic way that thoughts swirl round and round inside your head. Before you become a Buddhist you think it is easy to dodge developing bad habits, because you need only avoid doing things too often. Afterwards you realise that your life is shaped by your mind and you can screw yourself over by developing a bad habit with very few physical repetitions by repeatedly thinking thoughts

If you find this hypothesis worthy of consideration it greatly complicates the question of the effectiveness of affirmations. You have repeated thoughts that you haven't chosen and aren't much aware of. Your affirmation replaces some of these but not others. If you try to analyse the effect of an affirmation purely in terms of it own positive content, without considering the negative thought it displace, things could get very confusing.

When Scott Adams says to himself "I will become a syndicated cartoonist" is that instead of saying "I will become a doctor and cure cancer" or instead of saying "Only fine artists can become cartoonists."