The longer synopsis should also highlight the dramatic turning points and tell the reader of any other salient information which will help convey what kind of work it is, how well imagined are the characters involved and how well thought through and alluring is the plot.
This is different for non-fiction. Make each word in your synopsis count. In addition to letting a professional reader know what happens in your manuscript, the synopsis will also let them know at a glance if you have thought about how your work fits in to the market.
Second, a writer might genuinely be able to write a good book but not be experienced in the art of summarising a work in an effective manner. He disappears for a few days, but warms up to Bella upon his return; their newfound relationship is interrupted after Bella is nearly struck by a van in the school parking lot.
Need help to understand this trick in action? Also, you should be able to list any marketing opportunities you believe your book may have, such as identifiable, or even guaranteed readers such as students if you teach a course, anniversary tie-ins and so on.
So edit, edit, edit.