Isn't It Sometimes 'Planning for Disaster' that Brings Disaster to Pass?

[mythociate]

We all know the story of how Technicolor-Dreamcoat Joseph interpreted Pharoah's dream as a warning against upcoming famine. And--though I know it involved a drought or something else that only God can control--something in me wonders, 'Would the famine still have happened if Joseph had not convinced Pharoah to order his subjects to expect the famine?'

I think also of how it's been for me in so many places online. I'd get frustrated at the way people are doing things IRL, and write the further wrong things I expect them to go & do (usually intending it as a 'warning' to NOT do those things). And what happens? they go & DO do those 'wrong' things and/or point to my warning as a suggestion to do those very things! 

How much trouble could be avoided by not 'proclaiming it' until after it happens?