How do UFC refs know when to call TKO's?

If the fighter is unable to strategically or intelligently defend himself then the ref must stop the fight. Even if the fighter is getting beat up but not really all that dazed then that's not the ref's fault because the referee always, I mean ALWAYS and clearly tells them; "Remember to protect yourself at ALL times". So if you're not protecting yourself and somebody is pounding you while you're on the ground not trying to defend yourself and not trying to get out of there, the ref will probably stop the fight really soon no matter how dazed you are.