The quandary that I faced in one startup: the "old guard" don't know the product. Alternatively put the product they have been mind is not the one that exists nor is it the one that customers want. The "new guard" give the "old guard" the benefit of the doubt for a long time and become disillusioned/demotivated. The old guard doesn't like the new hires implications and ...

Of course it doesn't always pan out in this way but one or two anecdotes suggests it is not altogether uncommon.