Prince William has said that every celebrity he asked to back his Heads Together mental health initiative three years ago refused.
The Duke of Cambridge told the Davos World Economic Forum that "a lot" of stars were approached, but none wanted to be associated with mental illness.
He also said the wartime generation may have helped create some of the stigma.
People preferred not talk about such "horrendous" events, a stoic attitude passed on to their children.
The prince created Heads Together, launched to help combat the stigma of mental health, in 2017 with the Duchess of Cambridge and Prince Harry.
The duke told his audience of business leaders about his own struggles with mental health, saying there was one traumatic incident that he didn't think he would "ever get over".
He said if he hadn't opened up to colleagues about the situation, he would have "gone down a slippery slope" mentally.
Looking visibly emotional, he said he still found the incident "very difficult to talk about" because it was "related very closely to my children", George, Charlotte and Louis.
The prince has spoken previously about "very traumatic" callouts involving children while working for the air ambulance.
But he said such feelings were "only human", adding: "Yes, you put a suit of armour on… but one day something comes along closely related to your own personal life and it really takes you over a line."
The issue of mental health is a big theme at this year's Davos, with several sessions on the topic.
Studies show one in four people will suffer from mental illness at some point in their life, but many people are still too afraid of the consequences of speaking out or seeking help.
Despite a greater willingness to discuss the issue, the prince said that a lot of stigma remains, meaning "so many people are suffering in silence".
He added: "For some reason, people are embarrassed about their emotions - British people particularly," he told a packed audience at Davos.
He feels the British stiff upper lip that was common in previous generations has a lot to do with it.
The attitude was passed onto children, especially after the First and Second world wars when it became difficult to talk about "such horrendous circumstances".
"A whole generation inherited [this way of coping]. This was the way you deal with your problems: you don't talk about it."
But he said "a new generation knows that's not normal" and is becoming aware that it's better to be open about how they are feeling.
The prince urged companies to do more. "It should be so much easier to go to HR and talk about it. It has to come from the top."
Spotting the signs
During the debate, the audience was asked whether they or anyone they knew had suffered from a mental illness. Nearly everyone in the room raised a hand.
The Duke of Cambridge was at the forum with New Zealand's prime minister Jacinda Ardern, who has made tackling mental health problems a priority for her government.
She said it was a sad fact that everyone in New Zealand, a small country of less than 5 million people, knows of "someone who has taken their own life".
HSBC bank boss John Flint, also on the panel, said that in the "notoriously competitive" banking industry mental health problems were common.
He said it was imperative that people at the top spoke about it to allow those lower down in the organisation to open up.
"We all sit on the spectrum [of mental health]. I know there's a profound difference between when I'm feeling my best and when I'm not," he added.
Mr Flint said the bank was training managers to spot signs of mental health problems so they could help staff deal with them.
He said it made business sense given the impact problems had on workers' performance.