Do you understand everything about your OS? Your browser? Your user's browsers? Networking? Security? The short answer is no, frameworks are yet another level

Do you understand everything about your OS? Your browser? Your user's browsers? Networking? Security? The short answer is no, frameworks are yet another level of abstraction where some assumptions are made and [ideally] are well implemented/tested. My long answer would be: try to understand how it works, what are it's assumptions and what does it do differently/similarly to other frameworks; but do not try to understand down to the code, unless you spot and dig for a bug or are interested in collaborate with its development.