In any matter of tactics (military, chess, sports, etc) there are two basic coaching theories. One is a proactive mindset that looks to establish the pattern of action in the way most conducive to the identity of the coach's side. It is the tactic of strength. The other is more reactive; it looks for weaknesses in the other and exploits weaknesses.
Both can win in any contest. The most recent example of a reactive team winning a major title would Chelsea in the Champions League. In the Olympics the United States Women were proactive. They knew their strengths and maximized those. It lead to direct and physical play by the Americans. Both coaches were right to do so.
It is a basic theoretical question. It is the question of white or black in chess. Despite the fact that white holds the advantage there are masters who prefer to be black because it gives them the opportunity to gain insight into their opponent's mind. Others want initiative.
The same holds true in MLS. The LA Galaxy are probably the best at reactive soccer. Not only do they tend to bunker and counter; they do so to exploit weakness. San Jose does not concern itself with the weakness of the other. Instead they attack through paths well worn with the knowledge that their strengths even against a strength of the opponent.
Despite some conversation in the post regarding the attacking along the flank versus RSL the decision is not one of proactive/initiative versus reactive/exploitation. That route is a strength of Seattle and a weakness (of some degree and debated) for Salt Lake.
Where the concept comes into play is instead about Plan B. Plan A for both teams resulted in a draw. Being evenly matched these two teams draw often enough 4-4-5 in all competitions. The draw was expected.
On Thursday night Real Salt Lake will hold many advantages. It is their home where they've only lost four times in 2012 MLS play. There is significant elevation. RSL is playoff tested and their midfield played about 100 more games together than Seattle's midfield has.
Entering the time machine and reading about Sigi's game we saw a team that was about establishing initiative, grabbing territory and defending from front to back. The old Plan B was to force the other side to make mistakes that would then exploit weakness. It is about an orientation of thought that can be used in defense and attack.
Plan A for RSL is a narrow diamond with throughballs up the middle. Plan B for Salt Lake tends to the counter. Jason Kreis' orientation is both of initiative and exploitation. They win many games through this.
Seattle's Plan B for this match may need to shift. Flank play is the strength of the Sounders and a relative weakness of Salt Lake. Mistakes in Plan A exactly result in Salt Lake's Plan B.
What can be route two? Seattle has used moments of individual greatness as a tactic (Feed Fredy!), set-pieces (above average in dead ball situations), quick counters (Gspurning to Montero to goal), pressure defense (Sigi's Game), central play (Tiffert or folding in Mauro - ugh) and of course others.
There are 10 steps to win at chess. They basically read like a way to win at soccer. Tactics (in game decisions) as opposed to strategy (average shape, squad rotation) will determine victory on Thursday.
Leg Two will be decided by coaches, even if it is a special moment. Sigi Schmid's Plan B will heavily influence the result. Or it could be that the Plan Bs match up and everything goes to penalty kicks.