Attitude
The shelter was not limited to just having walls and a roof, alongside some drinking water. There were a number of cards pinned to each wall, as well as the roof, with special tools called Activation pins.
Some cards needed guidance, but other cards did the exact same thing regardless of who used them or what they wanted to do. If that was the case, did the cards that required no guidance really even need a caster? Shouldn't channelling aether into it be enough?
The answer was no, otherwise any random aether fluctuation could activate cards randomly, and that would be disastrous. There were, however, ways to keep cards active without the presence of a caster, and Activation pins were just one of them.