We have to do everything we can to protect ourselves, but at the end of the day, we still need the Mercy of G-d.
Some people like to feel like they are safe. They took every possible measure, and now they are invincible. G-d likes to remind us from time to time that we are still in His hands, regardless of how we convinced ourselves otherwise.
Reminds me of the famous moshel from Rav Shalom Schwadron: a crossing guard shows up at a busy Bnei Brak interesting and directs traffic for hours every day. But he doesn't realize that there is a traffic light above his head. He lets cars go when it's green, and he stops them when it's red. He thinks everyone is going because he directed them to go. But he doesn't realize that everyone is laughing at him, because he thinks he's directing traffic when in truth everyone is just following the traffic light above him... We are the same we. We think we are getting stuff done. But in truth, it's Hashem Who is doing everything, while we convince ourselves that we are in control.