That's kinda ironic really. Those who still remember him no matter how fondly also remember how he could stir up a honest's nest on a dime. He got mad quickly, and often, it seemed, without significant provocation. But when the time was right, he was the first to caution against that catastastroke.
I think I get what he meant. Maybe he didn't live his own words as well as he could have but that can't make his point wrong. We're all hypocrites to one degree or another yet that doesn't condemn the good we do or the best things we say. I think what Grandpa meant was actually fairly simple. Don't make things more than they are, and when things get tough, just relax and deal with it.
So go out there today and deal with your work or your chores or what have you. And if things go poorly, well, deal with it. Don't have a catastastroke.