“It was advertised that the Devil was putting his tools up for sale. On that date the tools were laid out for public inspection. They had prices marked on them, and there were a lot of treacherous instruments: hatred, envy, jealousy, deceit, pride, lying, and so on. Laid apart from the rest of the Devil’s tools was a harmless-looking tool, worn more than any of the others and priced very high.
“What’s the name of this tool?” asked one of the customers.
“That,” the Devil replied, “is discouragement.”
“Why have you priced it so high?”
“Because discouragement is more useful to me than all the others. I can pry open and get inside a man’s heart with that when I cannot get near him with any other tools. It’s badly worn because I use it on almost everyone, since so few people know it belongs to me.”
Even the most successful, spiritually mature people face disappointment and discouragement. The challenge is to honestly face the problems without fooling yourself or giving up, but rather acknowledge your need for help, get help from others and obey God in the midst of problems. 
“Life is filled with difficulties and perplexities,” King Solomon concluded, “and there’s much that nobody can understand, let alone control. From the human point of view, it’s all vanity and folly. But life is God’s gift to us and He wants us to enjoy it and use it for His glory. So, instead of complaining about what you don’t have, start giving thanks for what you do have—and be satisfied!” 
 John W. Yates II, Preaching Today, Tape No. 42.
 Warren W. Wiersbe, Be Satisfied – Ecclesiastes.