You have a chance for that pip to be a power pip, which counts for two pips if you use it on your own school's spells. (This is why you don't want to have too many spells in your deck that aren't from your own school.) The percentage chance of getting a power pip instead of a normal pip is listed in your character stats (hit 'C').
If you cast 1-cost spells every round, you won't really accumulate pips. Be sure to have enough Zero-cost spells (blades, traps, shields, etc.) in your deck.