refers to acts of service for others that go beyond what is required or expected. The expression probably comes from the Bible, when Jesus declares in his Sermon on the Mount, "Whoever forces you to go one mile, go with him two." (Matthew 5:41, (NASB))

But then Wikipedia accurately notes that:

The verse is a reference to the practice of "impressment" which, among other things, allowed a Roman soldier to conscript a Jewish native to carry his equipment for one Roman mile (milion = 1,000 paces, about 1,611 yards or 1,473 metres) -- no easy task considering a Roman soldier's backpack could weigh upwards of 100 pounds (45.4 kg).

"Going the extra mile" is thus not a feel-good Hallmark Card. As Wikipedia used to note:

Jesus' point was that his followers must relinquish their individual "rights" in order to advance God's kingdom through self-sacrifice.

We as Americans don't want to hear that last point. We don't want to "relinquish our rights." We don't like to hear anything about "self-sacrifice." Perhaps that's why the most recent edition of Wikipedia removed that last line and substituted this:

The editors of the New Oxford Annotated Study Bible have suggested that going the second mile would perhaps spare another from such compulsion.

In other words, "Don't ask ME to go the extra mile -- make my oppressors go the extra mile for me." Self-centered Americans. Wikipedia (and the New Oxford Annotated Study Bible) thereby completely negates what Jesus was saying. Turns it upside down and backwards. 

If you want an example of "oppression," imagine Jews in first-century Israel being subjected to military occupation by unclean pagans from Rome. Then imagine Americans having their one-party government of Democrats and Republicans replaced by members of ISIS.  

Are you ready for that?

Do you think the government will protect you from ISIS? Mitch McConnell is not going to grab a gun and personally protect your neighborhood from ISIS. He might conscript you to grab a gun and go protect someone else's neighborhood from ISIS. Will you obey the government and go fight ISIS? Will you be like the "zealots" and attempt to overthrow the military occupation of your "homeland?"

Or will you obey Jesus?