It is neither possible for a man with no experience of warlike operations to write well about what happens in war, nor for one unversed in the practice and circumstances of politics to write well on that subject.
So that as nothing written by mere students of books is written with experience or vividness, their works are of no practical utility to readers. For if we take from history all that can benefit us, what is left is quite contemptible and useless.
Again, when they attempt to write in detail about cities and places the result must be very similar, many things worthy of mention being omitted and many things not worth speaking of being treated at great length.
This is often the case with Timaeus owing to the fact that he does not write from the evidence of his eyes.
Walbank Commentary