Why is it important to check the source? For the same reason that, when someone adds a reference to a paper, or a wikipedia article, people will often follow the reference and look for where it is exactly that it says what the referrer says it does- and complain if it turns out it doesn't.
So, for instance, if I mention that the minimax algorithm runs in time exponential to the number of nodes in a game tree, and you ask me how I know, and I reply that I read it in the 3d ed. of "AI: A modern approach" by Russel and Norvig, you are well within your rights to open the book, search for this information and, if you fail to find it, ask me whether I'm sure I got my refs right.
And that is true regardless of whether my claim about the running time is true or not- because that's only half the claim. The moment you add a reference your claim goes from "X is true" to "X is stated to be true in Y" and you have to be able to prove that "X is stated to be true in Y", not just that "X is true". And if "X is stated to be true in Y" is not true, but you go on to assume "X is true", then any other claim you make after that is up in the air, because you haven't yet told us how you know that X is true.
Which is important to know, because once you screw up your facts, as you inevitabley will, you (and everyone else) can at least trace your error back to all the things that you know, and the sources you drew that knowledge from, and have a glimmer of a hope to identify the error in your thinking.
Accordingly- if someone claims that "I memorised X from Y", you can check that X is stated in Y. If it is, then fine. If not, not fine.
For instance- his article on wikipedia mentions that he "enjoyed approaching strangers and showing them his talent for calendar calculations by telling them on which day of the week they were born and what news items were on the front page of major newspapers".
I assume he did that throughout his adult life, so when he was in his 30s an 40's, in the 1980's and 1990's, how would the person he approached this way check the news that Peek told them were on the front page of X newspaper? They couldn't very well google it on their iPhone back then.
Besides, this is not very clear in his wikipedia entry, but it seems to me like he made a living out of his skills, so you know, it was at least partly entertainment (without trivialising, or in any way shape or form ignoring, the fact that the guy had obvious disabilities).
So I'm saying, when a guy tells you he can recall for you a bunch of facts you dont' really remember yourself and you can't very easily verify, and by the way you're welcome to a donation, you can take what he says with a big pinch of salt.
People are downvoting you, maybe for manner in which you're expressing skepticism, but a lot of the issues you bring up are a constant concern in psychology. For example,
1. Clever hans, a horse that was supposed to answer people's questions, turned out to just be responding to auditory/visual cues (seeing people gasp).
2. In the book, Mind of a Mnemonist, the author documents a guy who uses a memory technique to remember a lot of information. However, the guy also plays up the idea of his having synesthesia (crossing of perceptual modalities, like "hearing" visual things, etc..). The author is concerned that some of the things the guy says are motivated by his desire to make a living as a performer.
3. A lot of cases, like Kim Peek, raise the same concerns about the person being made larger than life, for whatever reason. Or the person having learned (whether intentional or not) some very specific skill for remember certain types of information. With practice, a person can learn to memorize phonebooks pretty quickly.
Often it's clear that people are exhibiting exceptional memory, but teasing apart the exceptional bits among media hype, people having a lot of unaccounted study time, and past accounts gets pretty tricky.
I'm a bit surprised at the downvotes. I've said things I thought would get downvoted in the past and in the end it turned out I got more ups than downs. But today, in this thread, they're pouring down like rain and it's very unusual.
So, quite aside from the fact I'm losing my high score (hey, I like a game like the next person) I guess I've said a few things that people strongly disagree with. I wonder if it's what you say- the way I express my skepticism, but I'm not commenting in a different style today than in other days. If anything, I was even a bit more guarded today than usual, because there's the matter of disability and all.
I think what's up is that people know Kim Peek as the Rain Man, from the movie, a guy who had a severe disability but nevertheless had an amazing talent, and they're upset at me for saying that maybe he was faking it after all (edit: faking the talent, not the disability; and I'm not even saying he was faking it, just that, like you say maybe he was made larger than life).
The way I read them, a few of the comments in this thread are basically saying that, cooks and entertainers aside, Kim Peek was the real deal. Well, I don't know the guy. I googled him, I looked him up on wikipedia. There are some claims of extraordinary ability. But, if he only did the same things that entertainers do, then his skills were not that extraordinary, only unusual. The fact that he had a mental disability makes them more unusual, but still not so far outside ordinary human potential that he should really get his head scanned by NASA.
So I dont' think I'm being unreasonable to remain skeptical, and demand evidence. I think what's unreasonable is that most other commenters in this thread are simply demanding that I agree with them, just because they know and everyone they know knows that what they say is the way they say it is. Well- sometimes you just have to stop and think how you know what you know.
You don't think given his fame, that his talents were rigorously tested and verified?
Does your comment mean you know why NASA (and others, I guess) thought he was legit?
What do you mean "why I came in here"? I post here very frequently.
Likely mid-western colliquial (I'm from Indiana). It means that you originally posted with the sole thought of doubting it. It has no bearing on how often you are there.
For example, a regular at a bar might get told one day, "You came in here looking for a fight!" - it speaks of intentions, not frequency.
Imagine it like this: say you're at some mentalist's show, and she picks you out of the crowd. She asks you your birthdate, you tell her, she concentrates (silence in the audience) then suddendly she starts riffing off headlines from that day's newspapers. Why, she can even remember the crossword hints from the Times of Pallookaville! And even their answers! (well just one of them but-) Music! Lights! The audience clap their hands! The mentalist moves on to the next target.
Did you, at any point during all that, have any chance to challenge the accuracy of the mentalist's recall? Not really. Would you do it even if you could? Most people will dread so much being the asshat that ruins the show everyone paid to watch, that they'd never say anything, even if they had a tattoo of that damned crossword on their butt, solved and done.
And does it make any difference if you go back to your house and google the information and it's all made up? What 'you gonna do? Call up each one of those 1200 people who watched the show and tell them the mentalist is a fraud? 'Course it's a fraud. It's entertainment!
That's one setting and it's a bit formal, like, but ceteris paribus, the same goes for any situation where someone is pulling that sort of trick on you- the whole trick is to move fast and not give the mark time to think and react.