nazanin saryazdi I couldn't tolerate her, so I left the room. I couldn't tolerate her = I wasn't able to tolerate her Tolerating somebody is a process rather than a short action. Swan is probably referring to cases in which someone was successful in doing something on one particular occasion in the past.
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nazanin saryazdiI couldn't tolerate her, so I left the room.I couldn't tolerate her = I wasn't able to tolerate her
nazanin saryazdiMichael Swan also said that for specific ability in past we can't use "could", we should say"managed to".It's not a specific ability; it's an action that we try to accomplish and succeed in accomplishing.