Change is one of the three constants in the world, along with death and taxes. Entrepreneurs are the epitome of adaptability.

Entrepreneurs don’t get terminally frustrated when the market changes on them. They gear up for the new challenge.

They continually think of creative solutions—whether it’s market needs they may be the first to identify or ways out of their own business difficulties. They see patterns and business angles where others see nothing. And when a market fades on them, they adapt.

“You go into business originally because you have a great idea. But life changes. If you can’t change, you’re out of business. You can never rest, and you always need to try new things,” says Dave Ratner, whose own career could be the poster child for adaptability.

Ratner started selling soft drinks in an old gas station service bay in 1975. He added pet food after noticing that the supermarket shelves carried more pet food brands than sodas. If he was going to sell pet food, he reasoned that he may as well sell leashes and collars too. Dave’s Soda morphed into Dave’s Soda & Pet City, which recently opened its fourth location.

The soft drink side grew into case deliveries to small businesses. Soon he figured why not deliver coffee at the same time. He steadily added more supplies and even pets to the pet food side.

Then he got the idea for Doo Dissolve, a spray that dissolves the droppings of birds and reptiles so cleaning and disinfecting pet cages is easier. He sells Doo Dissolve under a separate business entity to pet shops and pet owners.

And just last October, he launched Logo Goes Here, partnering with an ad agency to create network-quality advertising for pet stores in non-competing markets. “I know this will be the biggest deal,” says Ratner. “The retailer doesn’t have to do anything but slap its logo on the ad.”

The secret to his oddly united career, he says, is “figuring out what your competitors don’t do and offering that service.” In other words, be adaptable to market needs.