If you were under say 30, you have a tsunami-sized problem coming towards you and you probably don't even know it.

That killer wave is the national debt.

Countries like people go into debt when they spend more than they have.

You and I buy things with the money we earn.

Governments buy things with money they get from taxes.

When spending outstrips revenue, the government is in the hole.

Right now, the hole is $17 trillion deep.

This is an incomprehensible number.

What is a trillion dollars? Let alone 17 or 20 trillion.

Common analogies like you'd have to stack $1 bills 67,000 miles high to reach the current debt.

Though impressive sounding, don't help much if at all.

So let's bring the problem down to earth.

Right now, most investors believe the United States is a safe bet.

They believe, in other words, that they'll get the money they loan to the US back with interest.

But this can't go on indefinitely.

At some point, investors are going to say, you have too much debt.

You're a bad risk. No more money.

What happens then?

We don't have to guess. We can look at Europe specifically Greece.

Investors were happy to loan Greece money until 2010,

when it finally dawned on them that Greece couldn't possibly pay them back.

Almost overnight, Greece became a very bad credit risk, and the economy went into a death spiral.

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