Abram and Lot came back to Canaan from Egypt with wealth. However, because of the wealth the land could not take both family anymore. It was the time to make a decision. At that moment, Abram conceded his right to choose to his nephew Lot. This was not avoiding decision-making out of fear. It was an action based on faith. Abram believed that God would keep his promise of land. In previous chapter Abram made a decision by sight and went to Egypt to avoid the famine. There, He learned that it was not the circumstances (land or water) but God who kept Abram safe. Through this lesson, now Abram made a choice to give his right to Lot. His principle was he put the relationship first. This decision was not to keep his flocks or possessions, but to keep the relationship (v.8). He was confident (v.9) because he knew that whether he go right or left, the promise of God will come true (Will of God) as long as he puts his faith and seek God first (Isa. 30:21). Based on his faith, he did not follow his culture and gave up his right. It was a decision made by faith not by sight.
On the other hand, Lot who experienced same thing with Abram on the Journey to Egypt and back to Canaan still made his choice by sight not by faith. He chose the well-watered land (Gen. 13:10-11). It was self-focused and greed-based decision.
So when we made our decision, we are to put our purpose and principles on God (Glory of God, Fear of God, Will of God), not on ourselves, and we need discernment, wisdom and temperance instead of polluted judgment and greed.