The term "survival of the fittest" was coined by Herbert Spencer in 1864 as a new way of describing Charles Darwin's theory of natural selection. From then on, it's been used to explain everything from capitalism to sports champions. In our modern world it boils down to this: the weak die and the strong survive.
But that definition tells us we have to be a bully in order to be our best. That definition is a myth.
In the real world, you don't survive because you're extremely aggressive; you survive because you can to change to meet the needs of your environment - to adapt.
We're taught that the dominant wolf is the pack leader. The aggressive stock trader, the persuasive sibling, the domineering boss - they all lead by strength and manipulation, forcing others to adapt to them. In our dog-eat-dog world this self-assured attitude is wrongly revered.
Despite having a strong pack leader social system, the species Canis lupus (aka the wolf) is endangered. The North American gray wolf once roamed most of the continental United States, but is now confined to the northern reaches of Alaska and Canada. The pack leader of the wolves may seem strong, but his aggressive nature is leading his pack off a cliff.
On the other hand, their close relatives Canis lupus familiaris (aka the dog) are doing pretty well for themselves. After many generations, these former wolves learned how to play a clever game of submission that convinced humans to give them food and shelter, and as such they thrive. Their only real threat, other than a few cruel owners, is euthanization, but that's a problem of overpopulation and a product of their success as a species.
Dogs found their true strength by being submissive. In their battle for survival, the fittest of the Canine lupus species isn't the aggressive wolf pack leader; it's the wolf that is willing to set that aggression aside.
The same goes for all species. As humans, the most important method of survival is the ability to observe, learn, and adapt to your surroundings (aka mindfulness). You survive by teamwork, relationships, and yes sometimes by being submissive, so your group - your species, your family, your friends - can all survive and thrive together.
That does not mean you give up all responsibility. It means you still speak your mind when it's something you know is right and just. It means you speak your mind, but it also means you listen.
Sometimes it means sitting back to allow the bluster of others play itself out. A self-assured, aggressive pack leader may be right once in a while, but if they're stuck on their own opinion, not willing to mindfully observe or learn from the changes around them, then they'll be wrong most of the time.
The next time someone's being an asshole just remember that their kind will fight alone and eventually become extinct while your kind... well we'll need your kind to keep adapting and evolving. Your kind is the fittest that will help our species survive.