Christopher Reeve allowed himself 20 minutes of self-pity every day after his accident (exclusive)

The directors of the upcoming Christopher Reeve documentary say that even after he was paralyzed in 1995, he continued to feel grief, but his family helped him move forward

After falling from a horse in 1995, he was paralyzed from the neck down. Superman Actor Christopher Reeve's relatives say the only thing he didn't do was wallow in self-pity.

According to the new documentationSuper/Man: The Christopher Reeve Story (in select theaters September 21 and 25), directors Ian Bonôte and Peter Ettedgui say the actor did his best to face each day with positivity, despite the challenges he had to face all day, every day.

“He gave himself 15 to 20 minutes of pity every day,” director Ettedgui tells PEOPLE what he learned about Reeve during filming.

“And that was it. Otherwise, it was like there wasn't a minute of the day to waste. He'd think, 'I'm sad,' but then you could almost see him calculating, like, 'That's it. Now it's time to move on.'”

The directors and Reeves' children thank the actor's wife, Dana, for helping him carry on after his spinal cord injury.

“My mother was perhaps the most extraordinary person to ever walk this earth,” says Will, 32, of Dana. “And it's a testament to her unique spirit that she lived every day choosing hope. She had a relentless positive attitude that wasn't artificial, it was simply her personality. And she helped our family keep going.”

He adds: “She was thrust into these unimaginable circumstances as a young woman, and my parents often joked, 'We're really putting the 'for better or for worse' part of our marriage vows to the test.'”

Although he maintained a positive attitude – and worked diligently to raise money for spinal cord injury research and make a difference for the paralysis community through the Christopher & Dana Reeve Foundation – the documentary doesn't sugarcoat how difficult life was for the actor afterward.

Related: Why Christopher Reeve's Kids Celebrate His Joyful Life in 'Unflinching' Documentary That Doesn't Hide His Mistakes (Exclusive)

In the film, which uses both home videos and footage from Matthew's previous documentaries about his father, Reeve can be heard talking about how much he wanted to die after learning he would never walk again.

“I said, 'Maybe we should let me go,'” Reeve said in archived footage. He said his wife responded, “I'm only going to say this once: I will support you in whatever you want to do because that's your life and your decision. But I want you to know that I'm going to be with you for the long haul, no matter what happens.”

He said she then said the words that saved his life: “You are still you. And I love you.”

Reeve lived for 10 years after the accident, dying of heart failure in 2004 at the age of 52. In a cruel twist, Dana, a non-smoker, was diagnosed with terminal lung cancer 17 months later. The film also shows how Will, orphaned at 13, coped after losing his parents at such a young age.

Related: Robin Williams would be 'alive' if Christopher Reeve 'was still here,' says Glenn Close in new documentary

“Grief is final,” Will says. But he is proud of the work he and his siblings continue to do for the foundation, and he enjoys seeing his parents shine through Matthew and Alexandra, who are now parents themselves. He adds, “I think the most important element of the grieving process is healing, and healing can be found by honoring the people you have lost through the way we live our lives.”

The most important lesson he thinks they learned from the way Christopher and Dana went about their lives after the fall?

Will says: “We learned how important family and the love within a family are for a fulfilling and meaningful life.”

Tickets for Super/Man: The Christopher Reeve Storyvisit Fathom Events.

To read more about the extraordinary life of Christopher Reeve, pick up the latest issue of PEOPLE on newsstands Friday.

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