This seems to be a confusing point for new players that my group exposes the game too, as well. I have found that once you show the effects without the +/- symbol, like Regeneration, side by side with a card using the +/= symbols, the light bulb goes on in most cases that if it has a +/- they stack, otherwise the highest value effect takes place with no stacking.
Likely krj's response covered that, though. My apologies for belaboring the point!
