Proverbs 15:15

15All the days of the afflicted are evil,
But he who is of a merry heart has a continual feast.
-Proverbs 15:15

This proverb has a lot more to do with the perception of events in one's life rather than the events themselves. It is also important to state that when it comes to Scripture, evil does not always mean immoral. In instances like this, it is not saying that the days of the afflicted are immoral, rather, that their days are tormented or unpleasant.

For those who continuously complain and grumble about their day to day find themselves having constant reason to suffer. Yet, those who are merry and bright concerning that which is around them find cause to rejoice. Our outlook on our circumstances can greatly influence those circumstances. If we learn to praise instead of grumble and complain we will do much better off.