The difficulty is that by being overambitious, he has produced an uneven and carelessly written book.

Carelessly written or poorly documented monkey patches can lead to problems:

I know this letter is very carelessly written.

The book is carelessly written, and indifferently edited.

It is carelessly written with breathings and accents often given wrongly.

It was carelessly written, and exhibits no less than 81 omissions by "homoioteleuton".

According to Scrivener the supplied texts were very carelessly written.

A carelessly written memo might provide that much.

It is beautifully but carelessly written, without subscriptions at the end of books.

A carelessly written law, if taken literally, may be unconstitutional.