Chemistry.

When you're watching a production, whether on television or in theaters, when characters have chemistry, no doubt it makes the project complete.

It turns a fictional storyline into something that could be realistic, and viewers resonate with it in different ways. If you've watched Rizzoli & Isles, you can see Angie Harmon and Sasha Alexander's obvious connection on screen. They look like they could be best friends in real life.

The show needed this type of chemistry, and producers saw it almost immediately when they put the two actresses together. According to executive producer Janet Tamaro, Angie Harmon was cast first, and the relationship between Jane Rizzoli and Maura Isles was courtesy of their chemistry. She believes that their connection has always been the heart of the series.

"We cast Angie first, and then we had a tough time finding somebody who could stand up to her onscreen," Tamaro told Gannett in 2012. "When we put her with Sasha, it was just instant. They were playful. They were funny. They enjoyed each other. Tonally, it was exactly what I was hoping for, and it continues. When you put them in a scene, it's just magic."

Rizzoli & Isles is one of the best examples of shows showcasing women as fearless leaders. Jane Rizzoli wasn't a character who gave in to pressure or stayed in the background.

She took pride in being front and center, solving crimes as if her own life depended on it. Maura was the perfect co-starring character. The medical examiner added the right amount of softness to blend in with Jane's toughness, but do not be fooled — she also could get tough.

We're glad producers didn't rush to find an actress to star alongside Angie Harmon; the process helped the show in the long run.