Things consist of what makes them what they are.
These very constituents impose upon things their definitive limits.

Take life, for instance. It’s exactly that which makes the difference between a collection of inanimate chemical substances and a living organism which leads to its eventual demise.

Or our skeletons. And all our organs. They make us what we are and, simultaneously, set the limits of our existence.
Each of us can grow only that high, eat and drink only that much, sprint only that fast and live only that long.

Take our brains.
That’s what we think with. And we make errors with.
That we remember and forget with.
That we love and hate with.
That makes us aware of some things and leave so many others out of our knowledge.

That is capable to understand the nature of our limits and, too often, chooses to ignore that opportunity.