If you hang around on writing forums for a while, you'll discover that one of the guaranteed topics to get everyone hot under the collar (or rather the keyboard) is how - and why and how often and if - members spend time critiquing other members' work. Indeed, the only times a forum member - let's call him Caliban - has got their knife into me have been on that very topic, I should imagine because it is, exactly, a guaranteed recruiting ground for strong feeling among the members. (Though it didn't really work, because strong feeling is not always directed as its recruiter would wish.)
Why should this be? Clearly, critting each others' work is the way that writers have always learnt: no doubt Sophocles and Aristophanes swapped scenes in the pub over the retsina and calamari. It's not just that we all need an external eye cast over our work, and earn it by doing the same in return. Much more important is that one of the fundamental elements of learning to be a writer is to learn to stand outside your own work, and read it as another reader would who doesn't know what you're trying to say before you say it. And since that takes different muscles from learning to write, the best place to learn to control and exercise that capacity is on others' work. What doesn't work for you? Which bit? Why not? Why not? As a teacher I spend a lot of time trying to force people to get down to reading and discussing specific words, to do close reading as the literary critics say, because writers have to write specific words: all writing is close writing.
But still, new people join the circle or the forum, and put work up but don't comment on others. And eventually either they're taken to task for being all take and no give, or people just stop commenting. An egotist, people decide, only interested in themselves and what they can get. Meanwhile other new people happily dive in and comment but don't post their own work in return. This is likely to cause less trouble, but a writer who's willing to crit others without laying themselves out in return is also, ultimately, not a full member of the crew, because part of the coin of such intimate relationships is equal vulnerability, equal exposure.
But when the right phase of the moon comes round and a bout of forum soul-searching asks what's going on, a rather different picture emerges. There is the occasional, lazy egotist who assumes that everyone will love their work, but they've usually got bored (or mortally offended) and vanished by now. Of the rest, the story isn't quite so simple. Some non-commenters say that they'll post work and be grateful for feedback, but feel their opinion isn't worth having about others' work. It's not their genre/topic, or the standard's so good or the writers so experienced, they don't dare: why would their opinion be something the writer would want? Some non-work-posters feel that they're keen and experienced readers and will say what they can about others' writing, but that asking anyone to read their own work is an act of monstrous egotism: why would anyone bother?
All writers are egotists: we assume that what we have to say is worth hearing even unto a publishing contract, which is egotism of no common order even if it is chiefly indulged in private at home. But egotism operates oddly in groups which are, as the phrase 'writers' circle' implies, set up to connect equals, not pivot on a single ego. Which do you think is more worth having, and saying: your own words, or your opinions of others'? Which are you shyer of putting out there, bearing in mind that shyness can be a form of egotism since it can spring from thinking that everyone's looking at you? Where does your egotism lie?