-고서도 means "even after doing something", or "even under the effect of something". It has the implication that the given event normally would have made some impact but it actually did not. Note that 고, 서, and 도 each can be used as an independent verb ending. 고서도 combines these three senses. To briefly summarize, * 고 = 1) doing one thing before another (simple sequence), 2) doing something that influences another action. * -서 = 1) reason, 2) required first stage, for the action that follows. * -도 = 1) even if, 2) a gratuitous action (i.e. doing something when not required). Examples. - 축구를 두 시간이나 하고서도 지치지 않는다 = He's not feeling tired even after playing soccer for two hours. - 영숙은 두 번이나 이혼하고서도 또 결혼한다 = 영숙 is getting married again after having been divorced twice. -고서도 is similar in meaning to -ㅆ는데도 (하고서도 = 했는데도), but emphasizes the perceived impact a bit more. (-서 implies a completed action, so 하고서도 with no explicit past tense form implies the past or completion, like 했는데도)