Why is it possible to calculate the maximum error of a Taylor-polynomial with the Lagrange-remainder formula?

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We can calculate the maximum error of a Taylor-polynomial of n order with the following formula:

$$ R_n(x)=\frac{f^{(n+1)}(\xi)(x-c)^{(n+1)}}{(n+1)!}, $$

I know how to use this formula but I'm trying to understand more how everything works under the hood.

More specifically, why can we use the next n+1 term of a n-Taylor polynomial with a derivative value of $\xi$ to get the maximum error?