You want me to go take care of a problem with a troll? Cool but the troll has actually become an alcoholic because their companion was recently killed, and won’t stop drinking until you avenge this misdeed.
You try to gather information on the head thug who killed the Troll's friend and you come across someone with a stuffed troll’s head that won't tell you squat until you beat him at dice. To beat him, you have to gain the skills needed from another side-quest. After all that, the troll head enthusiast tells you that he doesn’t actually know where the head thug is but that local bandits at the tavern could probably tell you. This is almost every side quest (and some main quests) in The Witcher 2. Have fun footing it through since there's no fast travel!