2 Tim 1:7 

for God gave us a spirit not of fear but of power and love and self-control (-lit. “Whole mindedness”).

People are most easily manipulated when they are in fear.  Being in a state of fear short-circuts our reasoning ability (whole mindedness) and causes worry, which is the opposite of contentment.  Paul explains the secret of contentment:

Phil 4:11-13 

I am not saying this because I am in need, for I have learned to be content whatever the circumstances. 12 I know what it is to be in need, and I know what it is to have plenty. I have learned the secret of being content in any and every situation, whether well fed or hungry, whether living in plenty or in want. 13 I can do all this through him who gives me strength.