I don't actually write in first person a lot (make that I don't write fiction in first person a lot, it seems like a pretty natural choice for a blog), so this isn't so much a why-it's-difficult-to-write-in-first-person post as it is a things-that-bug-the-hell-out-of-me-when-reading-first-person post, I feel you should know that at the start, to save disappointment or confusion later.
And talking of things that are better known from the start... there are, to my mind, basically two types of first person story, narrative convention and told to an audience. In the former, the reader never really knows when or where or indeed why the character is doing the telling of the story, and it's entirely possible that the character never would actually tell the story, but as reader you have been beamed inside their mind and can experience it anyway. In the latter the narrating character is actually telling the story in some form, maybe writing a diary or telling a bar full of drunken revelers or at it's most extreme, telling the story directly to the reader (works okay for contemporary fiction, becomes rather weird for secondary world fantasy for example, as I for one am left wondering exactly how I got beamed into the swamps of wherever and why, having got there, I am being told the tale of this particular adventure and not concentrating on not getting eaten by malicious wildlife or something).
I don't actually have a preference, both styles of story can work perfectly well (apart from the direct to reader thing, which I find awkward and, paradoxically, distancing as it actually interferes with my suspension of disbelief), but I do tend to assume narrative convention unless told otherwise which is why I get annoyed when I'm suddenly informed at around page two hundred that what I'm reading is actually a diary found in the basement of an abandoned house or whatever the framing device I'm only just being told about might be. Actually there's a number of reasons why I get annoyed with that particular trick, as already mentioned, it's jarring, flow-breaking, it means I stop reading and readjust my brain to take this new perspective into account, but it also breaks my suspension of disbelief, or at least puts some pretty nasty cracks in it, because I immediately wonder how I didn't know this before. The thing is that people don't in general, tell things the same way if they're writing a letter or a diary or whatever. Little things like dates at the top of pages or 'Dear Cousin Emily' at the beginning are also a bit of a give away, and if those things have been left out, why have they been left out? Sometimes the author takes it upon him or herself to explain, which leads straight into my number one pet peeve with stories in the first person.
'I've been trying to tell this as a story, but I can't.' I've seen a number of variations on that particular excuse and they all make me want to throw whatever book I'm reading across the room. What this particular gimmick is supposed to do is make me think 'Wow. this story is so big, so real, it just can't be told,' but frankly I'm not that gullible, if a story is really that epic in scope and/or emotional depth I'd already have noticed, even if it's being told badly, and just being told 'this story is really epic' won't convince me any more than the reporter telling me that a supposed news story is 'fair and balanced' will make me ignore the blatant and extreme bias. But it's not just annoying because it's the author stopping the story in it's tracks to shout about how awesome a writer they think they are, it's also a demonstration that the author has missed what I consider to be the single most fundamental truth of story-telling :- We do not have to believe a story is real to learn something from it. Or to enjoy it.
Sadly I think that truth is being increasingly forgotten, drowned out by the flood of memoirs and the assumption that 'write what you know' means 'write what happened to you', but that is a rant for another time.