In this week's parsha, Avram tells Lot, his nephew, that it is time for them to go their separate ways. What caused Avram to separate with his nephew? A simple answer is that Lot's personality did not mesh with the personality of Avram. Avram always opened his house to strangers, regardless of their religion or moral values which might have conflicted with his own. Lot, on the other hand, was interested mostly in material gain. Another approach is that Lot might have been so bad that Avram could not tolerate him anymore. It is possible, though, to say that Lot was not so bad, because we see he left his home to go to Israel with Avram. Lot also developed qualities of hospitality similar to Avram, so we see that he was not a terrible person, and Avram had a good influence on him. So why did Avram wish to separate from Lot?
Rashi points out that Avram could not tolerate Lot's permitting his sheep to graze on others' property. In fact, Rashi records that Lot's shepherds defended their misdeeds and refused to concede that they were sinning. It would appear this is what Avram found intolerable about Lot. His refusal to admit his sins was a very serious personality flaw which Avram feared would spread like the plague to others in his household. Therefore, Avram wanted Lot to leave his home for fear of his influence on others.