Because every time you attack the Keeper, it attacks all the glyphs in front of it. Rather than avoiding the counterattacks all the time, I found it easier to just have one person taking all the hits (the 'bulletcatcher', and why they use Provoke), and have the others attack or heal as the need arises. The 'bulletcatcher's role is to stand there getting attacked all the time, either using sentinal, attacking or defending on his own turns.