[erur]

That doesn't mean you'd be trying to sell for lower prices, does it?

A (sufficiently rational) investor's willingness to sell is mainly a function of current price vs. expected future returns compared to other viable alternatives - which of course includes the dividends paid and any other benefits they might gain from ownership. And yes, there's also changes in personal need for currency, psychological reasons, etc. but I'd consider these special cases.

Even in your case if you had any good indication towards the stock you're owning being severely overpriced, the likely optimal thing to to would be to sell and dump the money into the next best alternative.

I'd also suggest to be careful in the assumption that "holding a stock forever" is a good idea. Very few companies have existed forever so far.