With every breath, you live an entire lifetime.
You are reborn, you live, and you die.
Between the rise and fall of just one breath, the entire universe---including every aspect of you---has changed.
Assuming another breath follows this one, your entire circumstances---where you are and what baggage you brought with you from the last breath to this one---are karma. Clinging to the thought that something remains the same or that there is somehow more than this is delusion.
Struggling with the questions such as "Why?" and "Who am I?", realizing "I don't know," and awakening to this very moment? That's one view of the practice of zen. Seeing your true nature this way frees you---but the "free" and the "you" may not be what you think they mean. Finding those meanings is, for some, also part of zen.