I aways wondered about that Elo Hell thing. If there are so many persons "stuck" in Elo Hell because of a bad team, how come those people never get in same team and, as consequence, have higher probabilitty of wining?
What I noticed in the games my team loses, the true causes usually are:
1) Ragers - they either leave, stay walking in base to not get detected as afk and keep trying to surrendering so he can play another match faster (sometimes even feed on purpose).
2) Leavers/AFKers - those that just leaves for stay afk for no reason, just for a big lack of consideration. If you are not sure you have enough time to play or if you may get interrupted in middle, don't queue.
3) "Ego Hell" - people call mid, call solo lane, call jungle. Sometimes, when they are just not doing very well, instead of swaping, asking help, warning that need to heal or anything else, they stay there. Sometimes, feeding, sometimes letting tower die, sometimes refusing help.
4) Lack of adaptation - people avoid swaping lanes or change his "build recipe" to adapt to enemy team. So many times I heard so many excuses I can't even remember. Ok, you can have a super deadly build. If you are GODLY DPS squish melee and they have a lot of cc and burst, you still need to survive to be able to even hit them. Better stay alive to dish 500 damage than to bet on "luck or death" for a small chance of dealing 1500 damage. Think about it, if the enemy team had such champ, who you would stun/focus/take out of battle first?
5) Lack of teamwork - people wadering loose on jungles when team is preparing to gank, people trying to be "Rambo", people flaming/raging about KSs (better to get a extra hand and make sure enemy don't scape, of that you don't die. In the end, the gold goes to your team), people pointing fingers as excuse to his own mistakes. All of those makes the teamwork worse and worse during game. The more blames and flames, lower your moral to suggest a plan and lower the will of the team to be united.
6) Lack of strategy - random ganks on bad positions (melees can't reach targets, team will be obviously surrounded and so on), people being baited, team entering in a bush when they KNOWS all 5 enemies are there, wrong champ acts as initiator, people trying to get kill withou measuring consequences (yes, you can kill that 100 hp feeing foe in the middle of the other 4... but you will probally die also... worth it? if your their team is in advantage, it don't. One more kill/gold for them... if your allies are dead... maybe some extra towers for them also).
If you and your team policy yourselves with the items above, you will probally win. Even if you don't, you can be sure it will be a really good game and worth it anyway, as both teams played well.