Today I'd like to share a bit of research I did when learning from Vlastimil Jansa's great book "Dynamics Of Chess Strategy", which I thoroughly recommend if you are a middle to advanced chess player.
He has a good way of writing by setting puzzles to understand openings and middle games better. Well, they are not puzzles as in "mate-in-3", but more "strategic decisions" based on his games.
Anyway here is one from the p.20 in the 2003 paperback in the Spanish Opening, Steinitz variation section. From a game V.Jansa-A.Zude Germany 1994 he asks you to assess what move to make at move 17?
As you will see he recommends 17.b4 which gave him a nice game.
He does so on the basis of Black not playing 17...axb4 and gives you an extra point if you saw
17.b4 axb4 18.axb4 cxb4 19.Bb6! Qc8 20.c5! dxc5 21.Nc4 +/-
However, when I played through this it just didn't seem right and I had a nagging feeling something was wrong. Sure enough, when I looked closely I found Black could improve at move 20
17.b4 axb4 18.axb4 cxb4 19.Bb6! Qc8 20.c5 O-O 21.Nc4 Bxa4 22.Rxa4 Rxa4 23.Qxa4 dxc5 24.Qb5 Nd7 -/+
Instead of a big advantage for White, it is Black that has a big advantage.
The moral of the story is to always check for yourself if you are not sure about a position. 99/100 times you find you are wrong and learn something new about chess - a tactic, a positional idea, or a dynamic theme. But once in a while, even if the author is a highly respected GM, you may be right!