(;
AB[pd][pf][pj][pq][qo][oo][cf][ck][cn][bp]
AW[dd][fd][jc][nc][qh][nq][kq][dp][cq][fp]
C[Black's response to the marked stone?

Source:
    American Go Journal, Vol. 27, No. 3, p. 11
    1993 Ing Chang-ki's World Youth Championship
    Stanley Chang (Canada) vs. John Lee (USA)
    Commentary:  Janice Kim 1p]
TR[qh]
(;
B[qf]
C[In the game, Black blocked here, which is in the wrong direction, because White still has an opportunity to invade the upper right corner.

The proverb to remember is "Don't block on one side when the other side is open."];
W[qj];B[qk];W[rk];B[pk];W[ri]
(;
B[rl]
C[Another mistake in direction.];
W[pi]
C[Now White has a strong ponnuki shape with access to the center.];
B[lc];W[pb]
C[And indeed in the game, White does enter the top right corner.

White went on to win the game.]
)
    (;
    B[pi]
    C[Black should have blocked here to put more pressure on the right side group.]
    )
)
    (;
    B[qj]
    C[Blocking on this side is better.  Black encloses the bottom right side.  Black cannot enclose the top right side with one move.];
    W[qe]
    C[The following is a likely continuation.];
    B[pe];W[qf];B[pg];W[qd];B[pc]
    C[The result is better for Black than the game line in the previous variation.]
    )
    (;
    B[ph]
    C[Black might also try playing on top with this standard move, but ...];
    W[qg];B[pg];W[qj];B[qk];W[qi];B[pk];W[rd]
    C[... White's territorially gain on the right side is perhaps too big.]
    )
)

