This quote means that we are all the same when it comes to life. We are all here for the first-and only-time. We are all here to make mistakes, to try and overcome obstacles, to learn as we go, and to succumb to whatever weaknesses our imperfect bodies fall under.
Think of the people that you work or study with. Once the front door of their homes is closed, you do not know what goes on inside. The faces of people hide their thoughts, ideas, fears, emotions, and weaknesses. The fact remains: We all have them. Hence, perhaps there is a good reason why the person who sits across from you is not the nicest person. There is hurt, death, pain, and need amongst all of us. Why add harshness to life?