Finding to whom a particular quote should be attributed is on the whole considerably easier than finding whether someone in particular said something we want to quote. Many wise sayings are often attributed to more than one famous person, but if we know the quote, running a search on it is a rather sure way of finding who, whether in the singular or the plural, is thought to have said it. (A rule of thumb is that if a quote is attributed both to someone famous and someone else considerably less well-known, chances are good that it's the less well-known person who should get the credit.) But working in the opposite direction is often unproductive. We remember a snippet of a quote, but because our memory isn't precise, we can't seem to get to authoritative "proof" of who said it. This is basically what happened to me nine and a half years ago when I tried to find a quote from the Communist Manifesto. Working from memory, I was able to reconstruct only part of the quote, which caused quite a bit of difficulty in ultimately finding it.