4 Social Security mistakes that can cost you thousands of dollars. Here's what to know.

Social Security supports more than 70 million Americans, ranging from retirees to disabled people and children. But it's also an incredibly complex system, with an operations manual that is 20,000 pages long, covering a tangle of 2,700 rules that can easily trip up claimants and cost them tens of thousands of dollars in lost benefits.

Some of the pitfalls are detailed in a new book, "Social Security Horror Stories," by Boston University economist Laurence Kotlikoff and personal finance writer Terry Savage. In some cases, the errors aren't the fault of beneficiaries, but stem from the Social Security Administration's own missteps. Yet claimants have little recourse for fixing the problem or otherwise protecting themselves.

There's a lot at stake in improving the system, Kotlikoff told CBS MoneyWatch. Social Security is often a person's biggest financial asset aside from homeownership, and the steady stream of monthly income keeps millions of seniors from slipping into poverty. But the program can be opaque and, perhaps unintentionally, encourage certain choices that cause people to lose out on tens of thousand of dollars in benefits, Kotlikoff said.