Rich don't sell, they leverage

[Mary Jay]

Ive heard many times: "Rich dont sell, they leverage". 

Than a lot of other people do "Buy low, sell high" sort of thing...

What is the benefit of never selling? Lets say you have a 100 year old house that is not in a super great shape, would not it makes sense to sell it when market is up and buy something newer?

I guess what are the advantages of never selling? 

Lets say you dont want to sell...You refinance it again, but then you may be get stuck with a property that you have a mortgage on for 100K but its worth 50K because the market is down and you refinanced it when the market was high, and now you have a problem..

I am trying to see if I am missing something...

Thank you, guys