Every situation presents you with two paths. You can choose the path of reaction or you can choose the path of action.
The first path is not really even about choice. It is the abdication of choice to every little event. You might leave the headlights on overnight. Or the photocopier jams. Or you spill ketchup on your blouse. The first path allows these events to bring you down, because you simply react.
The second path is the path of choice. It is about choosing how you want to feel. Dead batteries, jams and stains won't bring you down because they do not factor into your choice. If you choose to be happy, you will still be happy. These little events will still be inconvenient, but inconvenience is not the same thing as misery.