All of the titles of the tales in Dan Simmon's Hyperion make sense, except for one: in chapter 5 (page 246 of Mass Market Paperback), Sol Weintraub's story is titled "The River Lethe's Taste is Bitter."
I can surmise that
since the story is about Rachel aging backwards as a result of the Time Tombs, the bitterness is present. Still, most of Simmons' titles are either very literal or immediately metaphorical,
and the fact that this isn't entirely obvious is somewhat uncharacteristic.
So, I'm still not totally clear. Why is it entitled this?