As a very new player I lost my slightly less than 20 QL shovel by selling it. To me it was very valuable. I had started from nothing, and had built up mining and blacksmithing to be able to make it, and put a lot of time into improving it. Was it subjectively valuable? To most players, no, but to me it was. I didn't know what sell does - didn't know what it would do - but once that timer started I knew I didn't want whatever it was doing to happen, and I also couldn't figure out how to stop it.
I feel like the timer is there to give you a chance to say "I didn't mean to do that" ... but despite having been burned by this before, I did it again with another item later. And again, couldn't figure out how to stop the timer.
All I would have needed were:
1) a persistent message which says which item I was selling (because it's easy to have a random item highlighted, especially for new players)
2) a clear cancel button so you could stop it if you started selling the wrong thing.
I still don't know how to cancel a "sell" transaction if I start one. Do I click on the dirt and say "stop"? I thought I tried to hit the ESC button - but I don't think it worked. But in the midst of panic, I don't know what exactly I tried.