I'd say to an extent, yes. But bring too accepting of failure is unhealthy, just like the opposite being true.

too accepting of failure, unhealthy? Just like lashing out on defeats is unhealthy as well?

Yes. There's got to be a balance somewhere in between. Otherwise, one can never truly grow as a person.

Quite bluntly, yes you do have to learn to accept losing. No one in this world, no matter how skilled at something they might be, will lose at some point; and those people that got to those points? Imagine how many times they lost getting to there.

It's like a friend once said to me: "If you're winning all the time, are you really learning anything?" Sometimes, you need to get your ass kicked in order to learn as a player and become better. You take what you learn from losing, adapt to it, and become better. Nothing improves without failure, and as such it needs to happen in order for all of us to improve.

Losing sucks, I won't deny that. But people shouldn't turn into rage machines just because of it as that's not a healthy thing to do. It's okay to be upset sometimes about losing, but if you get angry all the time...it keeps compounding into worse reactions until, well...some of those journals and such you've posted. If you start getting angry at losing, then you should take a step away from whatever you're doing, have a moment to breathe and calm down, then decide if you want to go back. Games and stuff can be rage inducing, especially with the high competitive nature of most of them now...it kinda sucks but that's not something in your control.

Ultimately, yes you need to learn to accept and manage losing in games. You're not perfect, and no one else is; if they say they are that's bullshit. Teach yourself to literally learn from losing, and use it to make yourself better at the game so you lose less. Sometimes bad beats happen too, and maybe in team games its not directly your fault; in those cases just brush it off and try again.
When you start learning and winning from the things you learned by losing, then the wins will feel more satisfying. That's all I can really say about it.

On a scale of 1 to 10, how tolerant must I be on defeats? On Discord, someone said to me that it's a 1 on the tolerance scale, but I thought it's lower. And that can lead to frustration, which lead to doubt and anxiety and I feel like those are killing me, and my... inner peace.