A good idea that doesn't happen is no idea at all.
-- Louis Kahn

This quote is relayed by Richard Saul Wurman in My Architect [2]. I enjoyed the film and would recommend it to those with an interest, but some architects seemed to want less personal journey and more architectural analysis.

Wurman also mentions this quote in the April 2001 issue of design matters:

Louis Kahn said to me shortly before he died that an idea that does not happen is no idea at all. Late in his life, Mies van der Rohe told a student interviewing him about his work that the secret to his success was to "do good work."

Other mentions of this quote: 1, 2, 3, 4.

More photos at Google.

I also liked this exchange, from the film:

Nathaniel Kahn: I think you've built way more ... you've had way more success ... rate, in terms of your buildings that you --

I.M. Pei: [sighs] Oh, building doesn't mean success. Building ... three or four masterpieces [is] more important than fifty or sixty buildings. ... Quality, not quantity.