[rules-users] Rules confilct and resulution strategy

I am using Drools 5.5 and I have two drl files, i.e. Sample.drl, Sample1.drl, with four rules, two sets of duplicate rules. When I assert facts, rules from Sample1.drl file is getting fired. I assume in this situation rules are in conflict, therefore rules engine using rules resolution strategy firing rules loaded last to knowledge base. But I don't find any documentation indicating what leads to conflict in rules.  If anyone in mailing list has experienced similar issue, appreciate if you could share. Thanks,Amit