"And this gospel of the kingdom will be proclaimed throughout the whole world as a testimony to all nations, and then the end will come." - Matthew 24:14
A lot of people make a weird theology about reaching unreached people groups from this verse. Don't get me wrong, I absolutely think we should reach the unreached people groups, but I also think we should reach unreached people. The lost.
Some are called to crazy places where no one has ever been. But you're no less holy if you're called to your neighbor. Those who do not know the Lord are just as lost no matter where they are.
But I don't mean this to be a downer as much as a go-getter... Get out there and share. Not because you have any power over when the end will come (you do not) but because it is the difference between eternal damnation and eternal salvation.
And rejoice when everyone is reached. And then the end will come.