While most people require concentration to cast spells or prayers, those of the mage and druid class require the utmost focus due to the magical nature of their abilities.

Spell casting of any type can be interrupted by a number of factors, such as forcing the enemy to flee from a fight, or even stunning them.

However, any internal conflicts on a mage or druid’s part would result in an end of the spell that is about to be cast.

e.g. if you were to cast magic missile, then type cast forceshield before magic missile finishes, you would interupt your concentration and spell for magic missile would not be cast. (this is not the same for classes like cleric where it would still continue, unless you forcefully break the spell casting - move to a different room)

see also necro