Takes longer than you’d think. Trying to balance finding new markets with submitting new things to markets that have already rejected something of yours is likewise a little tricky. You don’t want to give up on one particular market, but you don’t want to get into a cycle where you get your stories serially (heh) rejected by each of three or four publishers in turn. Also, you know, there are all those submissions guidelines that you have to read: I mention this because I suspect that a lot of people don’t read submissions guidelines, and they probably should.
Still, productive enough work, in its way. Not overly creative, but productive. Also emotionally fraught, but you need to scar tissue yourself about that sort of thing. Life ain’t fair, and neither is the publishing industry.