"One shall not covet your fellow's wife, his manservant, his maidservant, his ox, his donkey nor all that belongs to your fellow man" (v'chol asher l'rei-echa). One may ask, after the Torah spells out that the prohibition of coveting applies to a neighbor's wife, and male servants and female servants, his oxen, his cows, his donkeys -- what is the summation "and all that belongs to your fellow-man" really adding?
The Meforshim explain, it is coming to teach us how to prevent jealousy towards a friend. One might look at a neighbor's wife and see how wonderful she is. One might look at his house and see how well he lives. One can look at his job and his children and think "This guy really has it made!"
The Torah is telling us to consider "kol asher l'rei-echa" -- look at the whole picture. Everyone has his or her own "Pekeleh" of problems in life. No one's life is perfect. As apparent as it may seem that this person has it 'made', we do not know the whole story. We can never know for certain. It is always necessary to take into account "kol asher l'rei-echa" [all that is doing with your neighbor].
Many times, when we learn about "all that is doing with our neighbor," we will not want to trade places.