Matthew 20:10-21
10 Now when the first [to be hired] came, they thought they would get more; but each of them also received a denarius. 11 When they received it, they protested and grumbled at the owner of the estate, 12 saying, ‘These men who came last worked [only] one hour, and yet you have made them equal [in wages] to us who have carried [most of] the burden and [worked in] the scorching heat of the day.’

The best way to kill contentment is to compare yourself with others. The workers in the story got discontent not because the master had not given them what they had agreed on, but because they compared what the others were given yet they worked shorter hours and that made them discontent with what they were given.

Galatians 6:4 (AMP)
4 But each one must carefully scrutinize his own work [examining his actions, attitudes, and behavior], and then he can have the personal satisfaction and inner joy of doing something commendable [a]without comparing himself to another.

When we start comparing ourselves with others then we open up our hearts to jealousy. In fact comparing yourself to others will lead to either you having a feeling that you are superior or inferior to others, it breeds either insecurity or pride. Paul says that each of us should scrutinize his own work; the problem is we start scrutinizing other peoples work and we neglect our own. We are different, gifted differently and with different callings and purposes.

The bible says in 1 Timothy that contentment with godliness is great gain. To be content means to be in a state of happiness and satisfaction. Are you happy with where you are in life? Are you content and at peace with where God has placed you and what He is doing?

The moment you start looking around and comparing yourself with others then you lose out on what you have and where you are because you are so busy looking over the fence and thus you end up being the one who loses out. This one thing I have learned in life, there will always be someone who has more than I do and there will always be someone who has less that I do. The secret to enjoy life and fulfill my purpose is to be content and peruse godliness.

Like racing horses we should wear blinders to keep us focused ahead on the race we are running lest we get distracted by looking around at the other horses and how they are running their race.