For an extreme example, say the VC invested $10M for 10% of the company, and then the company doesn't manage to grow, and gets acquired for the same $10M amount. The initial VC gets the $10M back from the acquisition (they make their money back, no profit). Then there is $0 left, and the common shareholders (early employees and often founders) get nothing.
It's a contrived example, and there are many other complexities to such a deal, but you get the idea.