Optimism. It can turn a situation that looks bad and bleak into something to learn from. It can replace those draining or negative thoughts of pessimism with something that will give you energy again!
And it can help you skip those obstacles you face so you can keep moving when you fall. Don't give up just because you have had a setback.
So don't just add this your own life but adding it to others in your life as well is a goo idea too. This is because you tend to get back what you give in the long run, and in the short run you will get to enjoy those smiles and know you have done a good deed by spreading optimism.