One of the slightly hidden mechanics of Ghost of Tsushima is that you can observe enemy leaders and captains before engaging in combat with them. This allows you to gain additional advancements to unlock your positions, powerful techniques that allow you to counter different types of enemies and weapons.
How to observe enemies
You can only observe enemies when they are unaware of your presence, so you have to be very careful not to be spotted. You will have to sneak very slyly through an encampment and approach within 25 yards of an enemy leader, if you wish to observe them.
Finding the enemy leader is much easier if you take advantage of your sharp senses. Press the touchpad to enter the sharp detection mode and you will be able to see the red outlines of enemies close to you. Enemy leaders will swing their weapons normally as if training for combat, and wear thick armor compared to the rest of the troops in the camp.
When you get close to the Captain, you will be prompted to hold the R2 button to observe them, and you will have to do so for five seconds, without interruption. Make sure no patrolling enemies are heading towards your hideout before doing so.
Remember that you can use tall grass to hide your presence, sneak under houses, on rooftops, and even wear specific armor that will give you bonuses for your stealth to make your job easier. It's worth doing this as often as you do, as it will double the speed at which you get new positions.
Every time you observe an enemy you will gain a step to the next position, then killing that enemy will provide another step. If you just kill the Captains and Leaders before you observe them, you'll only make half the progress to your next position you could take.