Everyone has their own idea of retirement. For some, it might mean downsizing to a smaller home that’s easier to maintain so you can spend your days however you want. Others dream of getting rid of a permanent home altogether in favor of traveling the country in an RV. Few people think of retirement as roaming the country in search of unskilled employment, taking on odd jobs that will give them a paycheck for a few months, or even just a few weeks.

But that’s the premise of Jessica Bruder’s book, Nomadland: Surviving America in the Twenty-First Century.

Bruder spent months embedded in this RV culture that exists all over America today. While there is a subculture of people who choose the life, most of the people Bruder spoke with were past what we would consider retirement age (in their 60s and 70s) and were living in RVs because they had lost their houses. Instead of renting apartments, they got by in mobile homes because it was cheaper and it allowed them to go where the jobs are.

For example, farms need extra hands during certain times of the year, and the times when there’s work to be had varies depending on the region, so those living in “Nomadland” need to be able to move around as work in one area dries up, so they can relocate to areas where someone might have work for them. This means everything from digging beets out of the ground to picking items off shelves in Amazon’s warehouses during the busy holiday season and getting them ready to ship.

None of these jobs are ideal for senior citizens. Many of them involve hours of hard physical labor and those with fitness trackers say they walk 12-14 miles a day, 6 days a week in the aisles of Amazon’s warehouses during the holiday season.

These are not the kinds of jobs the nomads held prior to retirement. Many of them owned their own homes, but lost them due to one financial mishap or another. Others lost money when they got divorced and were no longer able to rely on that second income. Still others had a 401(k) or IRA, but lost money when the stock market crashed in 2008 and pulled their money out of the market before it had a chance to recover.

Almost all of them receive money from Social Security, but it’s often not enough to even begin to cover expenses. Many of them only receive about $500 per month, which is barely enough to cover rent in some areas, much less other necessities like food, clothing and utilities. So they do whatever work they can to supplement their income.

All this is to say: you need a financial plan in order to retire. You can’t rely on Social Security and even just contributing to your 401(k) or IRA isn’t always enough if something happens to the market. Instead, you need to understand the basics of finances and how the market works so you can be financially prepared for anything that life throws at you. Because you don’t want to end up a 21st-century nomad.