One of the debates we get into in the martial arts is how "real" our training is, and thus, how well it will translate to real life situations.
One way we measure this in how intensely we train, how "alive" we train, and how much realism we inject into what we do. Some arts, such as BJJ, boxing, muay thai, and other competitive sport-like arts are well recognized for being "alive", with resisting opponents. Others will pad up and go full-bore as hard as possible, starting from day one.
Most folks agree that this sort of training is as realistic as it typically can get. But it's not perfectly realistic.
Most people bring up having a rule set in place as being why such training isn't realistic. That there "aren't any rules on the street".
I don't think that's a bad point, but I actually don't think that's the real reason why such training isn't perfectly realistic.
The main missing component to making it truly realistic is intent.
That is, the goal of winning a fight is different than the goal of seriously injuring or killing someone. Unless you are a sociopath or a sadist, you won't ever attack training partners with intent - that is, with the commitment to cause serious injury or even death. There is always going to be a part of you holding back, because you are a good person and don't actually want to hurt your training partner seriously.
I don't know about you, but I have no interest in training with sociopaths and sadists.
Even if we are not damaged in some way, it's not easy for many of us to replicate the thief, the rapist, the guy looking to mess somebody up - in our training environments. We try, but in our hearts, we don't have the same mindset as a real bad guy. We just don't.
So when we are talking about who trains "alive" and with "realism", we must always keep these caveats in mind. We can't perfectly replicate intent and the true bad guy mindset because we're not sick and evil scumbags.
We do the best we can, but it's still a myth that it's "realistic".