Approach one difficult situation in your life with a radically different mindset. How can you meet it with more humility? What lessons can you learn?
Think about one thing that you've always wanted to do, but were afraid because it pushed your limits. Reconsider your perspective on the task and go do it!
You don't have to swim deathly cold waters to prove you have determination. Adapt one new habit - consume less, take public transportation, conserve water, etc. - and stick to it every day.