I'm translating a book named "the Psychology of Selling", in which there is a sentence:

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But even though I hurried from prospect to prospect, and spoke louder and faster to each person, I was barely holding on by my fingernails.
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Here, what does "barely holding on by my fingernails" mean? Does it mean to keep the prospect or to stay in the trade for a living?

Looking forward to your help.

Calli.

Do inform me if you see any corrections needed in my written English.