What does it means to pursue happiness?

Henry David Thoreau's perspective of pursuing happiness 

In the text from Walden by Henry David Thoreau he describes happiness as the simplest thing in the world. For the author, to pursue happiness is to be in peace with the simplest things in life, and not to have stress. In the text he says " I wished to live deliberately, to front only the essential facts of life"  he is implying that for him the term happiness is just the things that make him happy. So by him pursuing happiness is the same that pursuing peace.