I am not much of a writer so forgive my mistakes.
I was working as a consultant many many years back and we were searching for computer software developers. The company was small about 25 people but things were good. They were making money. The Business development director kept a good handle on client ABC lets call them. Nerver went on new sales calls.
After about 3 years they, ABC gets a call and they are going with a new firm for their needs. ABC had about 90% of their work with this client and did not know what to do. Company is still around but had lots of lay offs and are trying to rebuild.
first time in years I had to look for new work
Please please do not put all of you eggs in one basket.