It's not hakuna matata, but according to my wife, I use the titular phrase all the time. I suppose that I use it in the context of excusing all the many minor infractions that all of us do in the process of living our lives, but that somehow don't amount to much. For example, the time when I accidentally turned left at the corner of my house, just like I always do, only to find that I turned one block early onto a one-way street, in the wrong direction. Fortunately, the road was completely clear and a simple U-turn took care of the problem. No harm no foul. But what if that had been the moment that the road was filled with oncoming traffic?
On a long hike more than 20 years ago in Telluride, CO, my companion and I got lost and ended up bushwhacking for more than twice the time we had intended. Needless to say, we didn't have enough water so we ended up drinking the water from a stream. I got giardia and thankfully nothing worse. I also didn't die when I slid down the side of the mountain. No harm no foul? More importantly, how pure must the water be for there to be no harm? The water was clear. So at least to the naked eye, it was pure. Pity that I didn't have a microscope on me to see the little bugs. Even then, I might have needed a mass spec to look for contaminants at ppm levels or lower which luckily turned out not to be there. Such an experiment would have resolved my drink or no-drink decision. Perhaps better, and easier, I could have carried a water purification packet that would have made the water potable. That's chemistry in action at the microscale of a single human, but the technology wasn't available back then. The real challenge is making such purification sustainable at the macroscale of our entire planet. That's when the titular phrase will be truly operative for all of us.