Actually, Buffett does not always hold stocks forever.

I think you may have misunderstood his meaning. IMO, what he meant by that statement that they want to buy great companies (at a fair price - which is another wonderful Buffet quote). His definition of a great company is such that there should never be a reason to sell it.

Of course, "never" is a relative thing in investing. Ultimately, I can't think of any company that will never be disrupted. And when they do get disrupted (think Blockbuster Video when Netflix took off), it matters how well they react and pivot.