The saying “when one door closes, another opens” is a quote from Bell. He ended the sentence with "but often we look so long and regretfully at the closed door, that we are unable to see the one that opens for us"
Source: yourdictionary.com, HuffPost (link to main source)
We all know the optimistic saying “when a door closes, another one opens” (in Spain also in the version “a door opens”).
The saying is a quote from Alexander Graham Bell who, after a series of initial failures in private and working life, had one successful life, with the first telephone patent and a series of studies on speech disorders.
His quote, however, does not stop there, but also concerns the need not to miss opportunities and to keep an open mind to new things.
“When one door closes another opens, but so often we look long and regretfully at the closed door, that we fail to see the one which opens for us.”
What Bell wants to teach us is not to fear change, because it can often be an opportunity to improve!