This week delivered calamities both unavoidable and avoidable. In the former category was the devastating series of tornadoes that swept through Moore, Oklahoma on Monday, killing 24, including 10 children. In the latter was the collapse of the Interstate 5 bridge over the Skagit River in Washington. The bridge's breakdown should come as no surprise, as it had been labeled "functionally obsolete" by the Federal Highway Administration. And we can expect more such tragedies, since one in nine bridges in America is considered "structurally deficient." The week also brought discussion of another avoidable calamity -- the negative impact civilian deaths from drone strikes is having on our national security. Unavoidable disasters will always be with us, which is why it's all the more important to avoid those we can, instead of pretending there's nothing to be done to prevent them.