Restaurants last three or four years if they're lucky. Banks merge and change their names at least every once every five year.
Entire neighborhoods change almost overnight.
Actually, about the only constant I can think of is Dog Day at the Fair. Every year, one week before the State Fair of Texas opens to the public, my dog Spot is treated like royalty by the concessionaires at Jack's French Fries. This has been going on for the past ten years. It's odd to think that a bunch of people working in a State Fair concession stand could be a source of stability in a city where close friends, favorite restaurants and even thirty story office buildings disappear with alarming regularity. It's true though.