Double hane does not force your opponent to take the outside ponnuki, but it means if he insists on keeping the corner he gets an inferior result to the joseki where you extend (sealed in and gote life). Can you see how to kill if black now tenukis?
Compare this joseki:
$$W
$$ . . . . . . . |
$$ . . . . . . . |
$$ . . . . 3 . . |
$$ . . . . 1 2 . |
$$ . . . . O X . |
$$ . . . O X . . |
$$ . 7 . O X . . |
$$ . . 5 4 6 . . |
$$ . . . . . . . |
$$ --------------+
- Click Here To Show Diagram Code
[go]$$W
$$ . . . . . . . |
$$ . . . . . . . |
$$ . . . . 3 . . |
$$ . . . . 1 2 . |
$$ . . . . O X . |
$$ . . . O X . . |
$$ . 7 . O X . . |
$$ . . 5 4 6 . . |
$$ . . . . . . . |
$$ --------------+[/go]
with (I finished with white gote to capture the ladder stone, which is honte and makes stone counts the same)
$$B
$$ . . . . . . . |
$$ . . . . . . . |
$$ . . . . O . . |
$$ . . . 4 . O . |
$$ . . . O O X . |
$$ . . . O X X . |
$$ . a . O X . . |
$$ . . 2 1 3 . . |
$$ . . . . . . . |
$$ --------------+
- Click Here To Show Diagram Code
[go]$$B
$$ . . . . . . . |
$$ . . . . . . . |
$$ . . . . O . . |
$$ . . . 4 . O . |
$$ . . . O O X . |
$$ . . . O X X . |
$$ . a . O X . . |
$$ . . 2 1 3 . . |
$$ . . . . . . . |
$$ --------------+[/go]
In the former white is open on the right side and black has about 10 points in the corner, in the latter the right side is closed and white is very thick there, and black only has 6 points in the corner; the only downside is the absence of a white stone at
a so black can exploit this weakness (with peep or cut or clamp or simply 1st line hane in endgame).
It is quite common for there to be a way for your opponent to resist your strategic plan of direction (here double hane saying I want to keep corner and give you outside), but he has to accept a local loss to do say. All these little losses add up.