The above video is graphic and shows people being killed. Watch it twice, so you can focus on several things. Specifically around the 0:14 mark where everyone started to lay down, because that's the universal signal for please come and shoot me.
Granted, these are gang members killing gang members, allegedly, according to the news reports associated with this video. That does not excuse the fact that they forfeited their lives.
They did not fail at the moment of that video, although it may seem like it. Their failure started that morning when they woke up. It started years ago when they decided to get involved in the drug / gang / violence game. It started when they took a step into the reality of the violent world without having any foundation into violence.
The lessons here is triple fold: Be ready for violence, expect a violent confrontation at all times, and never ever give up.
As Bill Rapier always says in his classes - "Carry your tools." If you do not have your tools you are DQ'ing yourself from the ability of doing serious work on demand.
Always be discriminating targets - everywhere you go, everyone you see, every place you go, you should always be assessing targets. Know who you need to look at, why, and what you will do when needed. You should be de-escalating your force, start at the top and work yourself down. This is how reality works.
Training is not just the way to survival, it is the only way to survive. Training instills confidence in your ability and the wherewithal to act immediately when required.
The video above shows a complete lack of all of those things, they volunteered for that slaughter. We can learn from it, and we will.