Strain represents how stressed, exhausted, or mentally overwhelmed you are. In game terms, its a resource that has to be carefully taken care of, just like wounds. But in reality, things that normally inflict strain don't make much sense, you would never pass out for stressing your body (unless under very specific conditions) to jump over to get cover, or from failing repeatedly, or from being hunted by your nemesis all day long. You might get really tired, but hardly will get unconscious unless you didn't actually eat or drink enough, which is another problem, not stress.
Exceeding Strain Threshold
When a character has suffered strain greater than his strain threshold, he becomes incapacitated until his strain is reduced so that it no longer exceeds his strain threshold. He is likely unconscious, or may just be so dazed and staggered that he's completely unaware of his surroundings and unable to interact with them.
States of Health
(...) A character is incapacitated once he has suffered more wounds than his wound threshold or more strain than his strain threshold. Incapacitation means that a character is unconscious and no longer able to act until the number of wounds he is suffering is decreased below his wound threshold.
Some things make a lot of sense, like stun grenades, electroshocks, being hit with nonlethal weapons, being thrown around the ship after a blast, etc. But you have to keep in mind that it is still a game and not everything will make sense.
Scathing Tirade (which causes 1 strain per success) is one thing that will never make sense, its a game ability that allows you to stress someone out to the point that they will become incapacitated (and likely unconscious). It's completely unrealistic, I know, but it's a fun ability, which is the point of the game.
How I would try to represent this stressing out in the game is that the character is so angry or frustrated that they do some kind of action that knocks themselves out, because they weren't paying attention to what they were doing. This introduces some jar jar moments in to the game, like the character blasting themselves on their feet, or firing a blaster without turning their battery safety on and it exploding on their face, or they walking right into a closed door and hitting their head. Each situation will call for a different accident, but that wouldn't happen if they weren't so stressed out.