Last KDnuggets Issue attributed this quote to Alexander Graham Bell (1847-1922)
When one door closes, another opens; but we often look so long and so
regretfully upon the closed door that we do not see the one which has
opened for us.
Carl Cook emailed that almost the same quote belongs to Hellen Keller (1880-1968):
When one door of happiness closes, another opens; but often we look so long at the closed door that we do not see the one which has been opened for us.
Who is right? Perhaps Bell said it first, and Keller added ?