his reach never exceeds his grasp
I need some tips to comprehend better this sentence: his reach never exceeds his grasp. I've read it in a review on the British historian Tim Blanning's new book called The Romantic Revolution: A History.
If you need more context, here they are: The book is a bit of a whirlwind tour, but those seeking a brief, nuanced overview of the movement will find in Blanning a knowledgeable guide—deft and incisive, but never facile. And although his goal is breadth, not depth, of coverage, his reach never exceeds his grasp.
Many thanks in advance!