ToME: the Tales of Maj'Eyal

I've just learnt a 'Disruption Shield' talent, but I can't activate it, and a talents list shows it as 'Unavailable'. What can be wrong with it?

Disruption shield is only available if your mana pool is sufficiently low.
Probably that is the reason.

Thank you. Didn't notice its description is scrollable. It says 'usable when below 25% mana'.

Good tricks for using this are to cast high mana spells repeatedly or even faster, use a bunch of high cost sustains then turn them all off. It gets harder to use as your mana pool increases to high levels after investing in Willpower and +mana items. But when you learn how to manage it, it's an amazing skill. Remember that when you're getting hit, other shields take precedence so if you're about to reach full mana and have your disruption shield pop, using a shielding rune or one of the Archmage shield skills or an items shielding ability will prevent that.

Thank you, Coldbringer. I've already finished a game by that archmage. But I'm thinking about an Insane difficulty, and I think archmage is possibly the best class for me to play a more difficult game than all I played before. So I hope to use your advice later.