A soldier is someone that does armed service for money. Today this means in a regular official force of a nation in difference to a mercenary that is a hired gun on a battle field. Most get into training with the age of 17 to 25 and only stay in that job for 5 to 10 years. Only few stay longer than 20 years.
Knights were nobleman that started training in early childhood even before they could walk. Those babies that started sleeping on their own in distance early from their parents where selected. Those that stood up for others naturally without being motivated by others and would fight, were trained in all arts from philosophy, religion, poetry and weapons use to commanding armed forces from hords of the commons to better trained organised men in arms, those that the word Gendarmerie derives from, to Gardists that lived in barracks and are as close as it gets to modern soldier special forces.
Knights declined and disappeared only as late as second world war. Their metal armour stopped being used way earlier when the crossbow turned the use of anything that slows down movement and needs time to put on and also off again, yet does not protect into a lethal trap, like in Ukraine tanks facing shoulder launched rockets.
Until than knights where nobleman and no Witchers. Witchers are the fantasy term for humans that have a special talent to feel their surroundings especially well, but without a totem a shaman would have. The U.S. army has records of entire units that avoided ambushes based on one soldier called sentinel feeling danger and warning the rest that did not feel any difference.
The only scientific explanation I have is following theory: The human brain has a filter that selects information. That is why we can follow a conversation in a loud club with the person next to us even so another person behind us is as loud.
For some that filter works different and the brain can process more incoming information faster.
If a terror group digged in bomb, they need time and the locals will watch it. They cannot warn the arriving foreign soldiers, because spotters will take revenge, yet they will behave differently no matter how often someone said "act normal" and some humans can spot that difference.
For toxics magicians this effect only happens on drugs. Ritalin is used to help kids to focus and all psychoactive drugs can have this effect, but not onto everyone in the same way. Ritalin is a form of an Amphetamine and they can turn one person into a calm listener and others into high puls unrests.
Secret Services know this and some use only toxic magicians almost like in the Shadowrun books. The problem is that all of these substances are also destroying the nerve system that is directly connected with our emotions and the ability to feel empathy and love. That's why junkies will betray their loved once to get more gear. Imagine what a CIA officer can do being in an organisation full of junkies that belief they can handle substances others don't even need to be calm in extremely dangerous situations.
Nobleman were called as such, because they were of better character and of course the bad guys will do a lot to pretend to be noble. Psychoactive drugs help to get there and during second world war when all major hard drugs where known, from Cocaine to Heroin created by Bayer to Speed and MDMA aka amphetamine and methamphetamine, they came to wide spread use in society, armed forces and secret services. Their long term impact is that it kills all noble in a human.
Cannabis products are called a soft drug. They come in sativa and indica. The first is stimulating and makes most laugh about all and every joke and the second is calming and helps against muscle pain from e.g. extended street sport activity or menstruation pain. They are both no narcotics and do not destroy the nerve system. They both stimulate it, which is for some difficult to deal with. If you don't like school weed will make it way worse...
A Witcher, like those sentinels the U.S. Army is aware of them existing, will be even closer to his surroundings and his brain will be able to process even more nerve impulses.
Witcher Knights to come...
