Whenever a caster attempts to perform a spell in Baldur's Gate 3, some of these attacks require their full attention to manifest. For example, a wizard trying to create a shroud of fog cannot summon the spell and then let it linger. They have to constantly think about this spell and make sure it stays active during combat. It requires a caster to maintain focus. If a spell requires a character's concentration, it continually holds it in place, but if that focus is interrupted, that spell dissolves and the caster must cast it again to summon it again.
Before using a spell, you can hover over it to see if it will require a caster's concentration. If so, it will say "Concentration: Mandatory" just above the range a caster is able to use the spell. Once used and summoned, at the top left of their party avatar, you can see an outline of the spell icon. As long as a caster is focused on that spell, it will remain in place, in the specified location.
Concentration is also required for some abilities. For example, a ranger, a minor caster, can use the hunter's mark on an enemy. If their concentration is interrupted, the spell fails and they will have to reapply it.
Concentration is also required for some abilities. For example, a ranger, a minor caster, has the ability to use the attack called Hunter's Mark on an enemy. If their concentration is interrupted, the spell will break and they will have to reapply it.
You can see how long these spells will remain active in the world by hovering over the effect and seeing the timer on the left side of your screen.
Be sure to read what spells and abilities require focus and, if they do, steer them away from the action. You don't want your caster to become subject to an enemy attack, disrupting the illusion he is casting to keep the ogre's attention busy while the other party members try to flank him.
