Though I find "life verses" to, on the whole, be silly, I do in fact have one. It is a verse that I find myself echoing at the oddest of times because it encompasses so much. What is this special verse? Romans 3:4, "Let God be true, and every man a liar."
The beauty of the verse to my experience is that no matter the circumstance, God's faithfulness is found true. I leave a better enumeration of the value of this verse to John Calvin,
These two things stand together, yea, necessarily accord, that God is true and that man is false, it follows that the truth of God is not nullified by the falsehood of men; for except he did now set those two things in opposition, the one to the other, he would afterwards have in vain labored to refute what was absurd, and show how God is just, though he manifests his justice by our unjustice. Hence the meaning is by no means ambiguous, — that the faithfulness of God is so far from being nullified by the perfidy and apostasy of men that it thereby becomes more evident. “God,” he says, “is true, not only because he is prepared to stand faithfully to his promises, but because he also really fulfills whatever he declares; for he so speaks, that his command becomes a reality. On the other hand, man is false, not only because he often violates his pledged faith, but because he naturally seeks falsehood and shuns the truth.”