When Stephen Dennis, a retired homebuilder in Bellevue was raising his two sons in the 1980s, he never heard the phrase “screen time”, nor did he worry much about the hours his kids spent with technology. When he bought an Apple II Plus computer, he considered it an investment in their future and encouraged them to use it as much as possible.

But things have changed with his grandkids and their Snapchat and Twitter.

“It almost seems like an addiction,” said Mr. Dennis, “In the old days you had a computer and you had a TV and you had a phone but none of them were linked to the outside world but the phone. You didn't have this omnipresence (无所不在) of technology.”

True, the anxieties these days seem particularly severe as, of course, they always have. Smartphones have a highly customized, 24/7 presence in our lives that feeds parental fears of antisocial behavior and stranger danger.

What hasn't changed, though, is a general parental fear of what kids are doing out of sight. In previous generations, this often meant kids wandering around on their own or slipping out at night to drink. These days, it might mean hiding in their bedroom, chatting with strangers online.

Less than a century ago, the radio set off similar fears, “The radio seems to find parents more helpless than did the funnies, the automobile, the movies and other earlier invaders of the home because it cannot be locked out or the children be locked in,” Sidonie Matsner Gruenberg, director of the Child Study Association of America, told The Washington Post in 1931. She added that the biggest worry radio gave parents was how it interfered with other interests — conversation, music practice, group games, and reading. In the early 1930s, a group of mothers from Scarsdale, N Y., pushed radio broadcasters to change programs they thought were too “overstimulating, frightening, and emotionally overpowering” for kids, said Margaret Cassidy, a media historian at Adelphi University in New York.

Then, television burst into the public consciousness with incomparable speed. By 1955, more than half of all U. S. homes had a black-and-white set, according to Mitchell Stephens, a media historian at New York University.

The hand-wringing started almost as quickly. A 1961 Stanford University study on 6,000 children, 2,000 parents, and 100 teachers found that more than half of the kids studied watched “adult” programs such as crime shows, and shows that featured “emotional problems”. Researchers were shocked at the TV violence present even in children’s programming.

By the end of that decade, Congress had authorized $1 million (about $7 million today) to study the effects of TV violence, moving “literally thousands of projects” in the following years, Professor Cassidy said. That eventually led the American Academy of Pediatrics (AAP) to adopt, in 1984, its first recommendation that parents limit their kids' exposure to technology. The medical association argued that television sent unrealistic messages around drugs and alcohol, could lead to overweight, and might fuel violence.

Video games presented a different challenge. Decades of study have failed to confirm the most widespread fear, that violent games encourage violent behavior. But from the moment the games appeared as a cultural force in the early 1980s, parents were anxious about the ways kid could lose themselves in games as simple and repetitive as a “Space Invaders.” Some cities sought to restrict the spread of arcades (游戏厅); Mesquite, Texas, for instance, insisted that the under-17 group needed parental monitoring.

Initially, the internet — known as an “information superhighway” that could connect kids to the world's knowledge — got a similar pass for helping with homework and research. Yet as the internet began linking people together, often in ways that connected previously lonely people, familiar concerns soon reappeared.

An author who surveyed 600 millionaires has claimed that she found the secrets of getting rich. Sarah Stanley Fallaw, the author of The Next Millionaire Next Door: Enduring Strategies for Building Wealth, got her findings after she surveyed American millionaires in 2015 and 2016. The book is a follow-up to her father's research in the 1998 bestseller The Millionaire Next Door, which Thomas J. Stanley wrote with William D. Danko.

Stanley Fallaw argues that resilience (抗逆力) in the face of refusal and strict goal setting are important to building wealth. "To build wealth, to build one's own business, to ignore critics and media and neighbors, you must have the ambition to keep pursuing your goals past refusal and pain," wrote Stanley Fallaw in the new book, according to Business Insider. She added, "Millionaires and other economically successful Americans who decide to climb the corporate ladder (企业晋升制度), or struggle to create a financial independence lifestyle early do so by pushing on without stop."

Stanley Fallaw stresses the importance of setting goals and sticking to them, especially for budgeting. She says that living modestly even as your income grows will allow you to devote a greater percentage of your income towards savings and building wealth. "Most millionaires we interviewed stressed the great freedom that comes from spending below their means," Stanley Fallaw writes.

The author says that the temptation (诱惑) to keep up with the spending habits of the people around can be highly harmful to building wealth. Particularly in the age of social media, when lavish (浪费的) vacations and new purchases are broadcast for the world to see, the perseverance (坚持) to live thriftily (节俭地) is important, Stanley Fallaw argues.

The famous scientist Stephen Hawking spoke at a science festival in Norway in 2017, “We are running out of space and the only places to go to are other worlds... Spreading out may be the only thing that saves us from ourselves. I’m convinced that humans need to leave Earth.”

Hawking was not alone in this view. Many experts feel that the only way for humanity to last far into the future is to colonize (移民于) other planets. That way, if a terrible disease, nuclear war or some other disaster strikes Earth, civilization as we know it would still have a chance. Mars is one of the most attractive destinations. NASA, the United Arab Emirates, the private company SpaceX, and the organization Mars One all have plans to send humans there. “Either we spread Earth to other planets, or we risk going extinct,” SpaceX founder Elon Musk said at a conference in 2013.

But not everyone agrees that colonizing Mars or any other planet is such a great plan. The most common argument against going is that it’s just too expensive or dangerous. It will take huge amounts of money and other resources just to get people there, let alone set up a place for them to live. It’s not even clear if humans could survive on Mars. One of the biggest dangers there is deadly radiation that ruins the planet.

Maybe all the time and money people would pour into a Mars mission would be better spent on more urgent projects here on Earth, like dealing with poverty or climate change. Some experts argue that handling a problem like an asteroid (小行星) strike or disease outbreak while staying here on Earth would be much easier and less expensive than surviving on a new planet.

In addition, moving to a new planet could harm or destroy anything that already lives there. Mars seems uninhabited, but it could possibly host micro-organism like. Human visitors may destroy this life or permanently change or damage the Martian environment. Some feel that’s too much of a risk to take.