|absorber (n., adj.)|
They can mirror that optimism or pessimism, but some absorbers may choose to "soak up" both.
If they choose to absorb the optimism, they may be seen stuck to the hip of the system optimist, if there is one. In this case, they'd be trying to help the optimist's goals to lift the system up to better, happier places.
If they choose to absorb pessimism, they may be stuck to the hip of the system's worrier or cynic, if there are any. They'd be trying to help with their goals to point out bad things that could happen and maybe even help disrupt system life.