Capa's Logic

I recently started reading Chess Fundamentals, by J.R. Capablanca.  As an aside, I am reading it with the e+Chess Books app for iPad and iPhone, and the app is truly amazing.  It's free, and comes with a free copy of Capa's book.  But, I digress.  Back to the point of my post.

In Chapter 3, Capa provides an example of a game where the winning plan consisted of relinquishing the initiative to obtain a material advantage, then weathering the storm, and then finally pressing the material advantage once the opponent's initiative has run out.  This is all well and good.  It makes sense.  But I am stumbling on Capa's reasoning of how he decided on that plan at the critical juncture.

The game is Capablanca-Janowski, Havana International Masters Tournament, 1913.  After 1.e4 e5 2.Nf3 Nc6 3.Bb5 Nf6 4.0-0 d6 5.Bxc6+ bxc6 6.d4 Be7 7.Nc3 Nd7 8.dxe5 dxe5 9.Qe2 0-0 10.Rd1 Bd6 11.Bg5 Qe8 12.Nh4, black plays g6, offering the exchange (e.g., Bh6 and Black's f8 rook can't move) in order to gain time and to obtain an attack.  Capa says: "Without considering at all whether or not such a course was justified on the part of Black, it is evident that as far as White is concerned there is only one thing to do, viz., to win the exchange and prepare to weather the storm.  Then, once it is passed, to act quickly with all forces to derive the benefit of numerical superiority."

What confuses me is the first part - without considering whether or not such a course was justified for Black.  If Black's course was justified, wouldn't following it result in a loss for White?  Or is Capa saying that if Black's course was justified, Black will win regardless of what you do, so you may as well fight it out with the plusses Black is offering?  I've just never heard or seen a high level chess player say that you should do something without considering whether the opponent's course of action will ultimately result in you losing.  Perhaps someone more experienced can shed some light on what Capa meant.

I'd guess he considered all other moves (i.e not taking the exchange) weaker, which is logically independent of the question whether Black's plan is justified.

pfren, thanks for your reply, but still why should white not consider whether black has sufficient compensation before deciding to accept the offer of the exchange?

Not if all other moves are weaker anyway.