Nature does not have to remind her charges to be positive. She does not need to remind them to be mindful. All the beings in Nature are positive and mindful all the time. It is part of what they are. You might say it is in their DNA.
Since humans are part of Nature, these two aspects of being should be also in our DNA. Yet many humans are not positive; they are depressed. Many humans are not mindful and in the present, their minds/ego keep them wholly in the past, reliving painful moments and events.
Allowing yourself to be outside, in Nature, and observing the life outside of your contained environment does breathe life into you. For moments, you can be conscious of nothing but what is around you in Nature. You have a sense of peacefulness and Oneness with what is around you.
Peace is inside you, and when you are in Nature.