In an age of crass reality LENS shows and viral video, almost anyone with the right combination of moxie, outrageousness, timing and exposure can claim a moment of stardom.

But then, as anyone in show business for the last few centuries can attest, determining who has staying power is an eternal mystery. A few recent overnight sensations, however, may shed some light on why some hang onto their mass embrace longer than others.

Susan Boyle, the frumpy contestant on the show “Britain’s Got Talent,’’ invited smug titters from the audience when she stepped onto the show’s stage in April. But when she opened her mouth to sing, the crowd was stunned into enraptured silence, and her moving rendition of the song “I Dreamed a Dream’’ became an instant hit on YouTube. But unlike many overnight Web sensations, her fame did not disappear the morning after. The Web video of her performance has been watched more than 310 million times, and last month her first CD became the fastest selling debut in British history while rocketing to Number 1 in the United States, Australia, Canada, Ireland and New Zealand.

Why is such an unfashionable and shy spinster, who up until last year did most of her singing in church, still in the public eye? Her undeniable talent is one reason. But as Ben Sisario of The Times added, “Ms. Boyle, who still lives in her family home in tiny Blackburn, Scotland, has what most YouTube sensations lack: a compelling story.’’

Like Ms. Boyle, the ongoing appeal of Captain Chesley B. Sullenberger III may also be rooted in his unassuming personality. After Captain Sullenberger landed his crippled Airbus on an icy Hudson River last January, he was hailed as a true hero by the hyperdriven media. And with other headlines dominated by scandalous politicians and Ponzi scheming hedge-fund managers, his quiet competence and understated humility struck a chord with the public.

Nearly a year later, he told The Times, his biggest surprise was not the attention, but that it “has lasted so long.’’

A similar sentiment was expressed by another previously obscure public figure when the initial glare of media attention failed to abate. “The fact that my 15 minutes of fame has extended a little longer than 15 minutes is somewhat surprising to me and completely baffling to my wife,’’ he said. Presumably, President Obama has by now accepted that his fame will not abate anytime soon.

Carmen Herrera, an example of a talented artist who is finally getting her due, would laugh at the term overnight sensation. At 94 years old, she has been painting fervently since the 1930s, but only sold her first painting in 2004. Since then, the Cuban-American artist has been hot, a rapidly rising star whose work has been added to the permanent collections at the Museum of Modern Art in New York, the Hirshorn Museum in Washington, D.C. and the Tate Modern in London.

So even in a youth-obsessed culture where fame can seem tawdry and temporary, maybe talent, professionalism and hard work do win out. In Ms. Herrera’s case, fame came to her soon after the death of her husband, Jesse Loewenthal, after 61 years of marriage. Some friends assumed that he was orchestrating her success from heaven.

Ms. Herrera balked at the suggestion. “Yeah, right, Jesse on a cloud,’’ she told The Times. “I worked really hard. Maybe it was me.’’

KEVIN DELANEY