Jaws was the first movie to generate over $100 million in theatrical rentals on its way to more than $400 million in box office sales alone. It created the new business model of heavily marketed, widely released summer blockbusters. It won three Academy Awards.

And it was also a mess.

Director Steven Spielberg started the film without a finished script or a working shark. He decided to film on the ocean rather than on a giant back lot tank, something that (for good reason) had never been done before. He didn't get the actors he originally wanted. He didn't film the story he originally envisioned.

During production, few things went as planned.

Which may have been the best thing that could have happened.

Few entrepreneurs wind up creating the products and services -- much less the companies -- they'd originally envisioned. No matter how thoroughly you research, analyze, road map, and plan, it's impossible to predict every possible outcome. 

Planning is important, but often your ability to work through challenges and adapt to changing conditions and needs marks the difference between success and failure.

Spielberg's ability to adapt to and make the best of a seemingly endless series of challenges and roadblocks? That's what made Jaws the film it became. 

Here are some examples as described in the documentary The Making of Jaws:

Spielberg wanted to direct the film Lucky Lady instead of Jaws. Studio head (and Spielberg's mentor) Sid Sheinberg "ordered" him to make Jaws instead. According to Sheinberg, Spielberg's attitude for a while was, "You're my friend. How can you make me do this fish picture?"

But he kept his head down and did the work.

Spielberg's decision to film on the Atlantic Ocean haunted the film's production. Logistical difficulties, equipment problems, and weather delays resulted in the film's taking more than twice as long to make as planned and costing three to four times what was in the original budget. 

But the result was worth it: As Spielberg said, "Lake water, pond water, tank water ... [don't] have the same texture or violence that the ocean has. This needed to be a convincing story about a great white shark, because if it wasn't, no one would believe it." 

The shark was the star of the film. In the original storyboards, the shark plays a prominent visual role during the attack on the female swimmer in the opening scene. But the mechanical shark rarely worked, causing Spielberg to invent creative ways to "suggest" the shark rather than show it: character (and shark) POV, part-submerged horizon lines, hurtling barrels, moving docks, etc. (In fact, the shark doesn't appear onscreen until two-thirds of the way into the film.)

What seemed like a constraint actually helped the audience make a genuine emotional connection. Experiencing the shark through the eyes and emotions of the film's characters causes viewers to put themselves in the same situation. The unknown is often scarier than the unknown; we've all been in the ocean and considered what might lurk below. As Spielberg said, "It's what we don't see that's truly frightening."

Spielberg wanted Lee Marvin to play Quint. Marvin turned him down. He turned to Sterling Hayden. Hayden turned him down. Actor after actor passed. Finally, he settled on Robert Shaw.

Who delivered the film's iconic Indianapolis scene.

But Shaw's casting was still problematic. The first time Spielberg tried to film the Indianapolis scene, Shaw was too drunk to perform well. He called Spielberg that night and asked, "How badly did I humiliate myself?" Spielberg answered, "Not fatally." The next day he tried again and, as Spielberg said, he "knocked it out of the ballpark."

When an employee makes a mistake, it's easy to forever view them through the lens of that mistake. Or decide to not give them another chance. Fortunately, Spielberg did neither. And that scene creates the emotional connection between characters -- and provides the "why?" for the character of Quint -- that gives the movie its heart.

The producers wanted real shark footage in the movie, so Spielberg hired Ron and Valerie Taylor to shoot footage of sharks off the coast of Australia. They built an undersized shark cage and used a 4'11" actor to play Hooper to make a 14-foot shark seem like a 25-foot shark. At one point a shark got tangled in wires atop the cage, thrashing and rolling violently. 

But the actor playing Hooper -- who was supposed to be killed by the shark -- wasn't in the cage. So Spielberg changed the script, having Hooper escape the cage, swim to the bottom, and re-appear after Chief Brody kills the shark. Even though not part of the plan, Spielberg was smart enough to embrace a happy accident.

Even after production was finished, Spielberg kept tweaking. He decided he wanted a scene where Ben Gardner's head floats into the hole in the boat. Since the film was already well over budget, the studio wouldn't give him extra funds, so Spielberg used $3,000 of his own money to building the hull of a boat and a special effects head and filling a swimming pool with milk to make the water seem murky.

The result? One more scream.

A final example: Since Spielberg and screenwriter Carl Gottlieb spent each evening of the film's production working on pages for what they would film the next day, the process was more collaborative than autocratic. As Gottlieb said, "You could talk with the actors about what they were going to say and they could supply suggestions, because actors study (and know) their characters more than anyone." 

Who knows a job better than anyone? The person who actually does that job. Spielberg's willingness to let his "employees" have a say in how their jobs were done added immeasurably to the end result: Chief Brody's iconic "You're gonna need a bigger boat" wasn't in the script but was was ad-libbed by actor Roy Scheider.

As Harvard Business School professor Howard Stevenson once said, "Entrepreneurship is the pursuit of opportunity without regard to resources currently controlled."

You may not have the perfect plan. Perfect employees. Sufficient funding. Extensive resources. 

But what you do have is yourself, and your willingness to work hard, embrace challenges, overcome roadblocks, and keep pushing toward your goal -- no matter what happens along the way.