Marcus believed that a man of 40 years saw just as much as a man who could live 10,000 years (see B7.49). So for someone who has been around a while, that person should not be surprised by much, if anything at all. As he says in this passage, "this is what you have often seen." When trying to prepare for the worst (premeditatio malorum), we should ask ourselves, "can it happen?" If it can happen, then we should be prepared for it to happen.
During this year of getting bit by a venomous snake, getting a cardiac ablation, having my father-in-law pass away, being flooded, having my daughter in a car accident ... it has helped me to cope to think, "any of these things can happen to anyone; why not me too?" And then I'm less surprised and awed and shocked to think of all that has happened to me.
And when you begin to discuss politics and religion and sports and all the other "stuff" - it's all been said and done before. The more I study history, the less the news is new to me. And lastly, it gives me a chuckle to observe people get all riled up about politics and religion. None of it is new and the world has seen so much worse than what we've seen the last twenty years.