The document categorizes types of complainers in 4 groups from least likely to most likely to take action:
1) Passives complain only to themselves and think it's not worth taking action.
2) Voicers complain to the company directly but may give the company a second chance.
3) Irates complain more widely to friends and competitors but also may give a second chance.
4) Activists are most likely to take formal action by complaining to authorities or third parties, with less chance of giving the company another opportunity.