A list of when you should and should NOT surrender.
(Note: I originally wrote a much longer version of this post but my computer decided to update in the middle of me typing it and I don't have the patience to type everything I wrote again.)
WHEN YOU SHOULD SURRENDER:
- Is the only thing standing between the enemy minions and your nexus, the inhibitors and/or a single nexus turret with 32 HP left, while the enemy team still have a decent amount of turrets left?
- Are you and your team struggling to get items while the enemy is getting them effortlessly?
- Is your team comp bad compared to the enemy team? (Is your team full AP, full AD, no peel, no tanks, triple ADC, ETC.)
- Is NO ONE having fun?
- Are you afraid that if you leave your base, minions will destroy the turrets and kill the Nexus, or that the enemy team will kill you immediately?
- Have you lost every team fight up until this point?
- If you press tab, does the enemy team look like this?

- if you press tab, does your team look like this?
(AFK)
If the answer to most of these was yes, then maybe it's time to call it quits and move on to the next game.
WHEN YOU SHOULDN'T SURRENDER:
- Is only one person on your team getting killed by the enemy repeatedly (Thus decreasing their gold and XP value)?
- Do you still have all of your Base turrets reasonably healthy?
- Are you able to contest objectives and defend without suffering too many loses?
- Are your main damage dealers only slightly behind and are able to keep up with the enemy in terms of Farm and CS.
- Do you have someone able to split push, take down turrets and give the enemy team a reason to deal with him/her and does your team have enough disengage to 4v5 while they splitpush?
- Have you won your fair share of team-fights?
- Can you leave your base without the fear of losing an inhibitor?
- Is there someone that can stay behind and clear on coming waves with little to no problem?
- Is everyone on your team on the same page and willing to wait long enough for the enemy team to make a mistake?
If the answer to most of these are yes then don't surrender.
Now I'm not one of those people who type FF@20 when my team makes a singular mistake, but I'm not also one of those "NEVER SURRENDER! WE JUST NEED TO WORK TOGETHER!" and I don't want to shame if you if you are like that. But sometimes winning is not an option and the game is over, sometimes your team-mates are, quite understandably, not willing to sit around for 40 minutes and wait for the enemy to throw and make a crucial mistake, sit on the side-lines while only one person is having fun and getting all the action or wait for their late-game hyper carries to finish farming. Just try and put yourself in their shoes and think how they're feeling. - Love to all, Sniperblp123
P.S: Remember that there is a pretty thick line between being annoyingly pessimistic and foolishly optimistic, this isn't a god damn anime folks where you can just say "As long as we believe in ourselves, the laws of physics, science and general common sense won't apply to us".