The call was unexpected. I'd talked with the client a good two to three years ago about the project but then they got busy with other issues and the matter died. I conducted some related research because the subject was of interest and I felt that at some point my work would pay off but then...nothing.
It is now revived. There are some twists and new factors but the project that had been pushed to the back of the storage room is out on the desk, ready to be dusted off and made exciting. Some work that was done for other clients in the interim has sharpened our perspective. We can spot aspects that might have been missed had we started when originally planned.
As with so much of life, you need to be patient and ready. What may appear to be lost is not really lost.
It is simply coming by a different path.