I've found sometimes I can force myself into "defense" mode just by stating to myself the opposite of what I'm trying to prove.

I may tell myself "it's impossible to use product X to accomplish this" then see that as a challenge and try to prove myself wrong. But this might only work because I can be an arrogant contrarian.

It's certainly a useful technique, but for best results you should spend most of your time in a more positive space: looking for things that work and how to get them to work better, leveraging your assets, etc. etc. Asset-based thinking suggests a 4-1 ratio; I remember reading a book once that had a complex model that claimed the optimum ratio was 3-1. Your mileage may vary.