Over thousands of years, human beings have been learning about more and more about this world, and have figured out many ways to avoid risks and make our lives easier. Even in ancient times, we used fire to frighten away animals, built simple boats to cross waters, and armed ourselves with sharpening stones and sticks. Nowadays, with advanced technology and instrument, people know the world better than ever. It's surprising how much people already know about this world and how much we've changed our lives by using the knowledge we have. But if you think we know everything, that's wrong. I guess sometimes we have to accept the limitation on our understanding of the world. No matter how much we're already known about the world, there are things that remain mysterious. I learned this from my pregnancy   which ended in the 6th month, due to a placental abruption  . I started to see my OB/GYN   every month, taking vitamins regularly, doing all the lab tests to make sure we were expecting a healthy baby. All the results looked promising, and we thought we would have a healthy baby girl in January next year. Even in the week before placental abruption, when I was in hospital because of a sudden bleeding, doctors didn't believe there were any bad possibilities after reading my blood tests. Unfortunately it still happened. Later, I asked my doctor "So what caused this?" She said, "I don't know. We probably will never know." After leaving the hospital, I sometimes do feel frustrated for what happened. But I already accept the fact that there are simply things that we do not know. No matter how well you plan and monitor your life there are uncertainties that can not be predicted and thus can not be avoided. _  Her name was Janet. She came to the world in April, and left us 6 months later. Though we never had the chance of meeting her, she is always our beloved daughter. In the late May 2013, during our first OB visit, we saw a little heart beating happily inside its mother. We couldn't even tell that was a baby, but we knew the magic was happening. The first three months was a disaster, Janet showed her power by making her mama throw up every day. Daddy became the cook of the family, and spent hours learning new dishes to please his picky wife. In the 12th week, we saw her again during an OB screening. When the doctor tried to measure her, she suddenly waved her hand to us, as if saying "I know you are spying on me again." Every regular OB check became our favorite experience, when we could hear her heart beating and knew she was enjoying herself. In the 18th week, one day when daddy was singing, she suddenly kicked her mama. We never felt so happy. Since then, she became more and more naughty, doing all sorts of exercise in her warm little house. We started to think about names, decorate her pink room, and shared the news with our friends. For young parents, there are always a lot to learn! Then it was the end of 25th week. A sudden bleeding terrified mama and daddy. After staying in the hospital for three days, things looked all right again, and Janet did not seem to be affected. However, the night after we went out of the hospital, a much worse contraction  started which caused placental abruption. When we went back to the hospital, mama survived from an emergency operation, but Janet's heart was no longer beating. Janet, thank you for all the joy you brought to us. We love you and we will miss you forever. Rest in peace! What does the writer mean by saying "  _  "?
We can not avoid risks and make our lives easier. We have to accept the limitation of human knowledge. We can change our lives by using the knowledge we have. We know the world better with advanced technology.