Authorship is a funny thing. Take this blog post, for example. There, above the headline, is a large, pink egg-shaped object that bears an uncanny resemblance to the putty-faced ovoid I occasionally wash when I can't see through the grime. It's my face, trapped in that awkward sneery half-smile, and these words are mine.

Well, are they? You could say that I've lifted "these words are mine" from the beautiful lyrics of Natasha Bedingfield's spectacularly written song about songwriting, "These Words Are Mine". And there they are, the same Roman characters in the same order, the same English words implying a very similar sentiment to that pop masterwork. I would argue, though, that since I haven't surrounded them with the lustrous beauty that Bedingfield did, I haven't so much borrowed them from her fair quill, but simply reproduced a familiar phrase.

I think that's fair enough, but it's hard to know. When writing something, you're aware that you might stumble across something someone else once did before, whether you're doing so accidentally or knavishly. It's the latter knavishness that is frowned upon, of course, for tweet jackdaws who end up cracking gags that others have made before, using their own avatar and getting all the plaudits.

But then, what if you come up with the same thing independently, simultaneously? There is only a finite number of puns, for example: someone's bound to have thought about the same one as you, and done it before – and probably done it better. Does that mean you're a thief if you think you've come up with one yourself, only to discover that it came out of the Ark?

I ask all this because, this week, words from Martin Luther King Jr echoed around Twitter and Facebook. "I mourn the loss of thousands of precious lives, but I will not rejoice in the death of one, even an enemy," he said. Or rather, he didn't. The quotation came instead from a Pennsylvanian English teacher in Japan, Jessica Dovey, who had followed her own sentiment with the true King quote:

Returning hate for hate multiplies hate, adding darkness to a night already devoid of stars. Darkness cannot drive out darkness: only light can do that.

Dovey's quote got added in to MLK's words, and then, for reasons of space in Twitter's 140-character limit, her quote became King's. Except he never said it.

Does it matter, now that we know a figure we admire didn't say these words – that they came from a pleb, someone who is just like us? Does it diminish their power? Does it erode credibility from those who repeated and retweeted the sentiment in those hours after the slaying of Osama Bin Laden, using the authoritative voice of a peace campaigner to reflect their views that the killing was less than morally perfect?

I think the answer is no. If anything, I feel it's a wonderful thing to discover a new, extraordinary quotation from someone completely ordinary. Would we have known about Dovey's words if they had not been wrongly attributed to someone more famous? Probably not. But I'm glad we did hear them.

It is too easy to attribute wise-sounding words to the wise people we've learned to admire. There are plenty of mistakes, bad quotes and less-than-pleasant things that got said by many famous figures whose other words are copied and pasted all over the place; but we tend to ignore those other sayings in favour of the aphorisms that suit our sentiments the most. It's a deal more complicated than that, but when you're trying to sum up your feelings in 140 characters or fewer, a lot of the richness to these passages does die away.

So, yes, I did write this; but I had help, from Natasha Bedingfield, from Martin Luther King, from Jessica Dovey. Would you believe me if I said I wrote this all on my own? Probably not. Does it matter if I did most of it by myself? I hope so. These words are mine. Trying to find the magic, trying to write a classic . . . sometimes we all borrow a little from somewhere else.