How do we Know?

How do you know? Some things in life have become so unclear I've begun to wonder how we are ever able to answer this question. With all the variables and, "What ifs," in life how do you know? Perhaps we are all aware of the basics such as our age or hair color but what happens when the foundation of who we are slowly rots away; all of our clarity pulled out from right underneath us? We begin to question ourselves. Am I truly the person I was two weeks ago or even two moments ago for that matter? As humans we are constantly changing and morphing to become what and who we hope but what if who we want to be counters who we were born to be?