Chess960: Opening Puzzle No. 10

Whoa, more than a year since I posted the last Chess960 puzzle! Well to celebrate the tenth chess960 puzzle, here is a real beauty. This puzzle has some important theoretical significance once you understand it:

SP486: What is the most important reason why

 1.d4 is not a very good opening move by white?

The answer is surprisingly simple!

Enjoy the solution given below

The answer is (drumroll)...:

1. Because the long diagonal a8-h1 is weak!

If you thought the answer was:

2. Because the king is exposed along a5/e1, 
white can easily defend against that and 
continue development with moves like Bd2/Nc3.

Explanation:

1. d4   ... b6!(b5)

2. Nf3  ... Bb7 

And now white's f1 bishop is thematically trapped, 

since moving either e or g pawn results in:

3. g3?  ... Bxf3 followed by ...Qxf3

if instead:

2. e3?! ... Ba6!

3. Ne2  ... Bxe2

and 4.Kxe2 is essential because if:

4. Bxe2 ... Qxg2 -/+