To expand upon NegativeCreepIsMe's comment, I think it is not only looking back on your life, but also regrets.
Most the thinks we end up regretting are thinks that we did not try because of fear. The fear of unknown, the fear of failure, the fear of others etc. etc. I think this is where the Clock metaphor comes into play. Each tick is another fear that you've allowed to control (steer) your life.
To expand upon NegativeCreepIsMe's comment, I think it is not only looking back on your life, but also regrets.
Most the thinks we end up regretting are thinks that we did not try because of fear. The fear of unknown, the fear of failure, the fear of others etc. etc. I think this is where the Clock metaphor comes into play. Each tick is another fear that you've allowed to control (steer) your life.