I’m frustrated. Look above the S in the word Stihl. See how its black on the cutting edge. That means the person who sharpened this chain got the metal too hot and it will no longer keep a sharp edge. My buddy, a professional tree trimmer told me this.
And it makes sense because the chain had a lot of life left in it when I took it to the shop to be sharpened, but when I brought it home and tried to cut Elm, it went dull very quickly. I tried to touch up the edge with my file but the steel feels different.
I suppose a person could cut a softer wood and maybe not notice, but Elm is one of the hardest to cut in our area. I put a new chain on my saw and it cut right through the Elm. It is truly amazing the difference a sharp chain makes. Now I’m thinking of the Abraham Lincoln quote. I don’t know how you spend four hours sharpening an axe, though.
Why do chains get dull besides regular use? Dirt dulls a chain quickly. This is why I usually lift logs off the ground with the bale carrier on my tractor. And if I’m not paying attention, another way to wreck a good chain is to hit metal, so I have to be careful not to cut through the log in a place where the metal bale carrier is underneath. Interestingly though, chainsaws cut through ice without getting dull quite well. Hence the hobby of some sculptors to use chainsaws to make ice sculptures.
Curiousfarmer 
I used to have my chains evened out every once in a while by a “professional”, but after an experience just like you described above I took it upon myself to sharpen them all with a file any time they need it. I find by paying attention to what I’m doing I can keep all my chains sharp and the cutters roughly equal in stature.
I guess I’m going to have to do this also, Edmund. I hate seeing an almost new chain ruined.
Now there’s irony! Thank you for this piece (or two) of wisdom.