Sam Gillian, a large man who is quick to smile, likes being terrified.

He thinks you should do the same.

“If you’re alive, you’re scared. That’s it,” said Gillian, 66, sitting in his spacious Tracey Towers apartment.

This is what Gillian has concluded from decades of teaching and research into how important fear is to human development. In the last three years, he’s published two smartly argued books — “The Beauty of Fear” and “Terrified by Education” — on the topic, and more are in the works.

His motive, other than an exciting post-retirement pursuit, is to open minds and make people happier. “If people realized that life is about being scared, we would function differently,” said Gillian, an energetic conversationalist. “We could reduce negative fear, and change it into positive fear.”

Gillian is fully aware he’s up against a big perceptional fight, but he’s confident his ideas are sound. Dan Liechty, an Illinois State University social work professor, agrees.

“Sam is undoubtedly a very gifted educator with an important and valuable take on the human condition,” said Liechty, a fan of Gillian’s work.

Gillian has always been drawn to people and how they think. The fifth of seven children, Gillian suffered from rheumatic fever as a child, and spent more time observing adults than playing with other kids. He drifted among various career paths — from the military to law school — before settling on teaching. Gillian started at a middle school in the Melrose section of the Bronx, and stayed for 21 years. “It was too much fun to leave,” he said.

Two things propelled Gillian on his quest to understand fear — a mouse and a dictionary. The former popped up in his apartment one night, scaring a man who thought nothing frightened him. The latter got him interested in the origins of words.

“If you look at the history of words, there is a commonality of meaning in terms of fear,” Gillian said. Frequently leafing through the dictionary during dinner, Gillian discovered that many positive expressions — like joy, awe, terrific, respect — all stem from Latin roots for fear.

He has since spent decades ruminating on how enjoyment and terror could be interlinked. The result is two, 200-page books and a workshop he gives at schools and conferences. Through both, Gillian strives to show how much of human excitement and development is rooted in fear, whether it’s roller coaster rides or marriage. By running from fright, Gillian argues that too many people deny themselves enriching, eye-opening experiences.

“I’m not against protecting ourselves, but we’re [overdoing it],” he said. “Sometimes it’s necessary for people to move away from their comfort zones.” In his second book, Gillian examines how societal institutions, especially in education, encourage this tendency.

Gillian points to his residence, Tracey Towers, as an example of how people play things too safe. Last year, Gillian withheld his rent until neglected repairs were made, and won a settlement in court. He has encouraged other tenants in the 870-unit complex to do the same. One neighbor recently followed suit, but he says the vast majority never act.

“I believe in being a troublemaker,” said Gillian, who offers to accompany tenants to court. “I think it’s a high art.”

Gillian spends much of his days writing and tutoring his 17-year-old granddaughter, who lives with him and his wife. He typically rises at daybreak for his pursuits, and is immersed for hours.

“This is the most fun I’ve had in my life,” said Gillian, who seems tireless. “I’m reaching people and getting them to open their eyes.”

Gillian publishes his books through a vanity press and distributes them at his workshops. He has sold over 2,000 copies of his first book, and the second is also moving along. As sales grow, so have the number of people who credit Gillian with helping them.

“Your message is powerful and timely,” said Edward DeBruin, a reader, in an e-mail to Gillian. “It has made a difference!”

Gillian is already on to other ideas, including a fictional exploration of fear for teens. Despite a tremendously successful “retirement,” Gillian stays humble and joyful — or terrified, depending on how you look at it.

“I don’t think of myself as a prophet or guru,” he said. “I just think of myself as a thinker.”