- Fundamental, economic sea change. (Instead of burgers, consumers opt to eat heads of cabbage for lunch on a permanent basis. Consumers opt to visit free, online theme parks or in other words, video games.)
- Erosion of business fundamentals.
- Prolonged, bad management - you just can't trust them and/or they are not capable, they appear to be sticking around.
In the situation of consumers switching to heads of cabbage for lunch, I would have to argue that McDonald's would adjust and accommodate and offer McCabbage. Still though, a permanent consumer taste shift could impact the business and diminish its long term prospects. In the case of a Disney theme park I would argue that Disney provides much more than a mere "theme park" experience through its established, proprietary environment of magical characters and moments establishing a deep, wide moat that is difficult for other businesses to cross.
Which leads to ...
The Erosion of Business Fundamentals
This effect will show up in the quantitative fundamentals of the company. Earnings per share will diminish over time along with return on equity. This will be a long-term, five to 10 year degradation, not an immediate microwaved result. It should be apparent that the business is not going to return to its heyday. In the case of bad management, shareholders and the board of directors should oust them but they may be around to stay.
Any of these situations, if permanent are legitimate reasons to seek higher ground.