"When you're younger and straight into the work force you're looking to have something to show for your work as quickly as possible," says Dillon. "The lure of a prestigious title and a bit more money fades very quickly. It's not enough to make us jump out of bed with enthusiasm for a job that's just OK."
As people approach their mid-thirties, they will have been working for more than a decade, during which time their priorities will have changed.
"By 35 people start to realise, 'This isn't actually making me happy and is this what I'm going to be doing for the rest of my life'," says Dillon. "They have other goals in life and they realise it's not all lining up."
Dillon, who authored the HBR Guide to Office Politics, says it's never too late to find satisfaction at work. A good place to start is by addressing the problem with your manager.
"A lot of people don't think about talking to their boss about finding new ways to stretch themselves," she says.
More responsibility and challenges within your role are one way to renew motivation, but it is also worth thinking about things you can do that are extra curricular.
"Volunteering through work and mentoring younger people are some ways you can make your day job more satisfying."
And while it can be tempting to jump into a career change when staring down the barrel of another four decades in a profession you dislike, Dillon recommends changing organisations rather than industries.
"Career change is an extreme nuclear option, because you don't want to waste all the years of experience you have built," she says. "I would look to take the skills you have built and find an organisation that would be more satisfying."
When moving companies, unhappy workers should pay close attention to the culture of their new firm, including their values and opportunities for promotion. If a complete reset is in order then a career change could be the best option.
"There's the old saying, 'Find a job you love and you'll never work a day in your life'," says Dillon. "If you find a job where you can have a work life balance, have colleagues you respect and a place where you like culture, then you do jump out of bed in the morning."