The primary thing when you take a sword in your hands is your intention to cut the enemy, whatever the means. Whenever you parry, hit, spring, strike or touch the enemy’s cutting sword, you must cut the enemy in the same movement. It is essential to attain this. If you think only of hitting, springing, striking or touching the enemy, you will not be able actually to cut him.
The McNamara fallacy, named for Robert McNamara, the US Secretary of Defense from 1961 to 1968, involves making a decision based solely on quantitative observations (or metrics) and ignoring all others. The reason given is often that these other observations cannot be proven.
The fallacy refers to McNamara's belief as to what led the United States to defeat in the Vietnam War—specifically, his quantification of success in the war (e.g., in terms of enemy body count), ignoring other variables.
In this sense, trust is a polarizing strategy, and it's one that is important to apply early on in the relationship before someone becomes important to you. If you trust someone excessively and it goes badly, but they don't matter to you, you can just kick them to the curb. In general, trusting someone at a level that seems slightly excessive for their level of importance to you will help you sort people in your life who you want to be more important to you than they are from those who you want to be less important than they are.
And it does need to be excessive. It needs to be trust beyond reason. Not beyond all reason, but somewhat beyond what currently seems reasonable. If it is not, then unless they are prepared to take the first move, you will never find the signs you need to move to a higher level of mutual trust.
Sometimes this will go badly, but you need to be able to try bad things.