Why do strangers believe quicker than those who know us?

Look how quickly the people of Nineveh believed when Jonah took the Word to them. 

Jonah 3:1-7(NKJV)

Now the word of the Lord came to Jonah the second time, saying, 

“Arise, go to Nineveh, that great city, and preach to it the message that I tell you.” 

So Jonah arose and went to Nineveh, according to the word of the Lord. Now Nineveh was an exceedingly great city, a three-day journey in extent. 

And Jonah began to enter the city on the first day’s walk. Then he cried out and said, “Yet forty days, and Nineveh shall be overthrown!”

So the people of Nineveh believed God, proclaimed a fast, and put on sackcloth, from the greatest to the least of them. 

Then word came to the king of Nineveh; and he arose from his throne and laid aside his robe, covered himself with sackcloth and sat in ashes. 

And he caused it to be proclaimed and published throughout Nineveh by the decree of the king and his nobles, saying,          Let neither man nor beast, herd nor flock, taste anything; do not let them eat, or drink water. 

Why is it that strangers believe quicker than those who know us best.  I guess it shouldn't be surprising since Jesus warned about it.  "A prophet is without honor in his own land".  :)