|Cover of Murray's|
According to this research, Murray attributed this quote to Goethe in his 1951 book The Scottish Himalayan Expedition (J.M. Dent & Sons, London). In it, Murray recounts leading the Scottish mountaineering team on their first expedition to the Kumaon range in the Himalayas the year before when they succeeded in climbing five of the nine peaks attempted. According to Wikipedia (I admit, not always a reliable source itself), near the beginning of his book, Murray writes:
... but when I said that nothing had been done I erred in one important matter. We had definitely committed ourselves and were halfway out of our ruts. We had put down our passage money— booked a sailing to Bombay. This may sound too simple, but is great in consequence. Until one is committed, there is hesitancy, the chance to draw back, always ineffectiveness. Concerning all acts of initiative (and creation), there is one elementary truth, the ignorance of which kills countless ideas and splendid plans: that the moment one definitely commits oneself, then Providence moves too. All sorts of things occur to help one that would never otherwise have occurred. A whole stream of events issues from the decision, raising in one's favour all manner of unforeseen incidents and meetings and material assistance, which no man could have dreamt would have come his way. I learned a deep respect for one of Goethe's couplets:Whatever you can do or dream you can, begin it.Boldness has genius, power and magic in it!While Goethe would no doubt have echoed Murray's sentiments (he comes close in Faust), the German writer did not write these particular words attributed to him. So who did? That's still an open question. It has been suggested that Murray mis-remembered them from a early 19th-century 'loose' translation of Goethe's work by John Anster but this is not conclusive.
Until such time, perhaps we can attribute them to the Scottish mountaineer who climbed to great heights in the Himalayas. At least you can point to a printed source although it will cost you a small fortune to obtain a copy of your own. It's been reported that Murray's book is out of print and commands prices in excess of £100 from antique book sellers.
But the point is, sources are important. Until we can identify a source, we can't honestly attribute words to anyone without misleading the reader or listener. That's why I urge storytellers to acknowledge the source of their story -- where did you find the story or from whom did you hear it? It's just common courtesy to recognise those upon whose shoulders we stand. I think even Mr Murray would have appreciated that.
Learn more about W.H. Murray and Scottish mountaineering at https://en.wikipedia.org/wiki/W._H._Murray and http://www.undiscoveredscotland.co.uk/usbiography/m/whmurray.html