I think this statement is true both for the book, Night, and also real life. Thinking about the possible consequences of actions is something that comes with growth, experience, and maturity, but there is no guarantee that the actual outcome will be anything like what we are able to predict.
Think about Eliezer's thought to save his gold tooth. At one point in the story he could have "sold" it to someone for an extra ration of food. In the end, the tooth is stolen from him for nothing. He knew the gold was worth something and hoped to hold onto it long enough to make it worth his while, not knowing that he'd lose it soon without a reward for it.
I also think about the hospital scene, when Eliezer's foot is healing and his father convinces him that they must leave the hospital with everyone else before the raid, or surely they will be left behind to die. How could they have known that remaining in the hospital would have saved their lives?
Of course I have never experienced anything as extreme as the Holocaust (and likely never will), but certainly there are parallels in my own life where I made a decision based on my belief of what the outcome would be, and I turned out to be horribly wrong. I believe this is one meaning of the trivial phrase, "That's life."