"Sentiment has immense power over physical reality by influencing human action. "

I already admitted that sentiment affects human action, but that's not the same thing as making rivers run uphill. Wishing your coffee was hot doesn't raise its temperature (but it may raise *your* temperature).

Reith's point was that the forbidden status of the Pnume charts was simply a taboo imposed in the self-interest of the Pnume. Looking at the charts wouldn't bring a bolt of lightening onto Zap's head. The fact that the Pnume would retaliate if they found out is a separate consideration. The charts possess no intrinsic magical powers, they are just tools.