E7 is easily defensed by D9. A move to C8 pretty much forces a response of C7 by H, and now V plays E7. Under this scenario, H's defense of D9 won't work at all, V just moves to D8 to secure the connection. Moves such as this are termed forcing moves, and understanding them is important. Another important concept in hex is the ladder.
Ladders occurs when both players place their pieces along one row or column.
They're usually forced by one of the two players, and they usually occur near an edge. 3-template on the right side with hex G7, prior to V moving to I6. When trying to connect to an edge, it is usually better to get an unassailable link to the edge first, then try to connect to the link. Play defense first, offense second - even when ahead. If you move first, you will win with perfect play.