The other level is this: why should the end matter? In achieving a goal (defined by the set of desireable criteria), there are many possible ends (solutions that achieve that goal by meeting all the desired criteria). Which end is ultimately selected and achieved should be determined through a process of good decision-making and action.

You should decide on the desired criteria (the goal) and then try to acheive those criteria in the best way possible; a good process will achieve the criteria the best way possible. If you instead take the criteria, select a solution (an end), and then try to achieve that solution (the end), you may not have chosen the best solution often because your biases are at play or because you're taking an opportunistic route.

What's actually happening when you focus on the solution instead of the process is that biases and opportunism are adding additional criteria to your goal (e.g. preferred ideological stance, least work needed, etc.) If these are truly desired criteria, then they should be defined at the outset and they should be part of the goal. By not defining them up front, it means that they are not sufficiently important to warrant consideration in finding a solution. That you then allow them to "sneak" into your solution's criteria without your knowing is the fundamental problem to focusing on the end and then selecting the means: you're unconsciously allowing criteria deemed to be unnecessary to factor into a solution.

Focusing on process ensures that the solution meets the set of criteria deemed desirable. If the focus is, instead, on the solution, the solution may meet additional criteria to those deemed desirable—by meeting additional criteria, you're further constraining the set of possible solution and perhaps excluding the "best" solution.

By focusing on the means, you do the morally right thing and you are more likely to achieve the "best" solution.