Dark LegacyWild surges and the concentration skill.
When a spell is near your maximum complexity, and you fail casting it, there is a slight chance of a 'wild surge'; a random magical effect. If you find your feet suddenly enlarging, bricks falling on your head out of nowhere or similar events, you have just experienced a wild surge! They are generally bad for your health.
Some classes can train in the 'concentration' skill. this skill lowers the chance for wild surges considerably and allows you to succeed more often at the complex spells.
The game also finds it under: wildsurge, concentration.