From my perspective, a raid leader needs to: Be Patient with people learning the encounter, remain calm throughout a raid, motivate the raid to continue after a wipe, not let real life affect how they play, determine what needs to be adjusted to prevent a wipe (as opposed to telling the people that caused it, what they need to do instead), replace players based on the needs of the fight, and explain fight mechanics. Above all however, a raid leader needs to understand that not everyone else thinks exactly the same way.
You will have people that can't manage to press the same 3 buttons for 3 minutes in a raid because: They're eating, alt-tabbed, talking on the phone, in the bathroom, cybering, trolling forums, in /tell wars, listening to music, had a hard day at work, got in a fight with their significant other, got corpse camped in STV, got yelled at because they caused the last 2 wipes, or are for whatever reason tired/upset/distracted/butthurt. Dealing with these people defines your leadership. I personally suck at it, and can't comprehend how being called a loot whore over vent causes someone to not be able to chain cast Healing Wave on the MT during Vael.
An amazing portion of "L2P" is "Learn to not get distracted and just focus on the fight"