Does what I think affect what I do or does what I do affect what I think?

Both, surely. Is there any reason to think otherwise?

If I think there's a mugger around the corner, I won't go there. (What I think affects what I do.)

If I'm prejudiced against midwesterners and I end up working with several smart, interesting, friendly people from that part of the country, what I think about midwesterners is likely to change; what I do affects what I think.

We could multiply examples indefinitely, but this should do.

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