Even though this principle isn't found in this or any passage of Scripture,* it's fully embraced by many Christians.
Mark 12:31 doesn't command us to love our neighbor's personality or have warm feelings toward him. It commands us to treat him with the same kindness and consideration we instinctively show ourselves.
Christianity is about putting God and others first, not putting ourselves first. And focusing on others is actually one of the most effective ways to overcome our own insecurities. (See Beatin' the Blues)
Philippians 2:3-4 sums it up this way: "In humility value others above yourselves, not looking to your own interests but each of you to the interests of the others."
"Loving ourselves first" appeals to our fallen human nature but it has no foundation in Scripture.
* Twisting Scripture is a common ploy of Satan. (See Christ's temptation and insights on His temptation.)
This is the first lie in the Trojan Horse Enemy series. You can read the intro to this series HERE. If you want to study more Scripture related to self-love , check out my Self-Esteem Posts. You can do a 5 minute Bite Size Bible Study on this devotion HERE.