Be soft. Do not let the world make you hard. Do not let the pain make you hate. Do not let the bitterness steal your sweetness. Take pride that even though the rest of the world may disagree, you still believe it to be a beautiful place.
Last year, I ran an inspirational newsletter for an educational business. This newsletter featured a new quote every day. I got a fair amount of practice at weeding out quotes that were misattributed or inaccurate in some way.
In general, people slap the wrong name on a quote because it is a way to get attention. Everone shares words of wisdom by Einstein, but who cares what Jo Shmoe said?
There are several ways you can smell a rotten quote, however. For one thing, people who wrote and lived a century ago were really not that pithy, I promise. They used more, and longer, words to express their point. If it's a succinct quote, be wary.
In the case of the above quote, I felt that our famous black humorist, Kurt Vonnegut, would never offer up something so hopeful. It just doesn't fit his tone. If he were to offer up something hopeful, it would not be so blatant; it would be layered with ironic observations.
Be wary of GoodReads. The quotes you find there are never verified. They are all user submitted. Even if you find a quote submitted by more than one user, it is still likely wrong. Some erroneous quotes have been entered a thousand times or more. Likewise, ignore BrainyQuote or any other quote aggregate. These places do NOT verify sources.
However, try out Wikiquotes. Quotes submitted there should be linked to their sources, where possible, and the discussions pages yeild further breadcrumbs on a quote's true origins.
It's ok to cite an unknown author. If you have done your best to verify a quote and just can't find its originator, it's best to admit that the author is unknown, rather than slapping a famous person's name on it.
"Author unknown" is different from "Anonymous." "Anonymous" means you have found the orginal source, say a newsletter or article older than any other reprinting, and that original printing has no name attached to it because the name was purposefully withheld. "Author Unknown" means you have no way to discover who published the original.
Translations are tricky. I tried to quote some translations and found them to be so widely varying in content that they were not useful, unless I had a published book and therefore a somewhat official translation. I found a lot of translations online by amateurs, some more pithy and quotable than others, and ultimately decided not to quote them unless specifically citing the translator in addition to the famous person being quoted.
A pet peeve of mine: funny quotes are often misattributed to Mark Twain. Mark Twain was not the only funny person in our history; in fact if you see a Mark Twain quote it is most likely to be WRONG. Go to the Mark Twain Project, UC Berkely's vast searchable archive of Samuel Clemmens writings, and search for your quote there.
If there is one thing I have learned from reading the Quote Investigator web site, it's that oftentimes there is no "one source." Something funny is written a long time ago, in the midst of a very wordy paragraph, and over time, people knowingly and unknowingly cite this witticism again and again, slightly altering words or phrasing; eventually we are left with something a good deal more succinct or pithy than the original. Those end up, say, in graduation speeches by people we've never heard of.
My final bit of wisdom, ironically, is a source-unknown joke of internet fame. Enjoy.