I'm gonna be a prick here real quick.
Doesn't there seem to be a bit of a definitional issue here? What does it even mean to be strong (or weak)?
Do wealth and control equate to strength? Personal power and physical might? Intellect and self control? It's kinda hard to define, as all of these things could equate to strength and yet also could entirely fail to be strength. There has to be a better way to define it.
To me, the problem with the quote is that it's sort of inherent. To me, being strong means having the ability to impose one's will onto the world, and thus on others. To be weak is to be at the mercy of the world and others. So the quote is basically saying water is wet.
Being able to do what you will makes you strong, suffering what you must makes you weak. How else would one define strength and weakness?
Double prick time.
But what does it mean to impose your will onto the world? To do what you will? What determines what you want in the first place?
You're born in a time and place you didn't choose, you're given genetics you didn't choose. You go through life encountering countless circumstances you didn't choose. Forming memories of things you didn't choose to experience. In response, you form your desires, your personality, and act as you do. All your wants are entirely determined by circumstance. In other words, you're automatically at the mercy of the world around you by existing.
After all, what could you even want if the world didn't present at least some bits of information to you? But you didn't choose that information, nor did you choose your inherent disposition for how you respond to it. What strength is there in that?
At the end of the day, all of us are at the mercy of the world and suffer what we must. Some of that suffering comes in the form of the actions of others, sure, but their actions were themselves at the mercy of the world.
To imply that there are the strong who do what they will and that there are the weak who will suffer what they must, seems to imply a belief in evil. After all, what suffering would there be if the strong were all good and kind?
But the truth, at least to me, is that we're all weak. We're all at the mercy of the world.