"The slow surf crawled and seethed in the dark and he thought about his life but there was no life to think about and after a while he walked back." What does this quote from The Road show the man is realising?
It is absolutely crucial whenever a question is asked about a quote to look at that quotation in context. This quote is a case in point. The lines immediately before the quotation reveal the context and also help the reader to understand what the man is experiencing as he hears the surf. The lines before read as follows:
Coughing. Coughing. He bent over, holding his knees. Taste of blood.
What is causing the man to think about his life and its value is that he is beginning to recognise that he is coming down with an illness from which it is unlikely he will recover. The taste of blood in his mouth is a sure indication that something is desperately wrong with his body, and the fact that he has to bend over and clutch his knees until his coughing fit subsides is another sure indication that he is suffering from a serious illness. The man, contemplating his life, realises that "there was no life to think about." This seems to indicate that because of the unspecified apocalypse that the earth has endured, the man feels that he has "no life." The focus of his life has all been about keeping his son safe and he has had no time or energy to live his own life.