Hagalaz is the rune that marks the beginning of the second aettir of Elder and Anglo-Saxon Futharks. It’s name is usually translated as Hail. That frozen precipitation that falls from the sky in some parts of the world. I have been in a few hail storms, and usually very small pellets of hail, about the size of BB gun pellets. Mostly I have been inside, where it does make quite the din, but apparently being caught outside in such a storm is unpleasant, although only mildly as the tine stones beat against your face, head and exposed skin, as their descent from the sky causes them to be moving at very high rate of speed as they accelerate towards the earth.
There is the other hail storms, where hail stones can be as big as baseballs or softballs, and these hail storm can do significant damage to property, people and animals, as they are also moving quite fast, and being larger, can pack particularly more destructive power when they do so. If you have been fortunate enough to not live through one, here is a google image search link to help you.

For me at least, that is the lesson of Hagalaz. Destruction. Destruction that leaves only things that can barely be salvaged in it’s wake. What is left after the Hagalaz storm? Well, apparently ice that melts down into water, which can be beneficial to any crops that survive of the beating, and not much else. It is after the storm passes that is the important time to rebuild though, because what is left, is strong. It is durable. It has withstood the storm and can continue forward. The weakness has been cast away and it leaves only room for the strong to grow, prosper and move forward. If you were to use Hagalaz against a foe, and that foe manages to walk away at the end, you better hope is lesson in survival taught him to think better then messing with you ever again, and perhaps to follow a new path. Otherwise, he won’t be so easy to eliminate if there is a next time.