The Comfort Motive decreases if your Sims spend too long standing up and working. It's not as important as other motives, but if it decreases too much, your Sim will become overworked and highly stressed. If your sim becomes ill, comfort is key to recovery and your sim must spend alot of time sleeping and relaxing instead of being on it's feet.
 How To Resolve
This Motive can be simply resolved by sitting on a comfy chair, or by going to bed. Some chairs, such as recliners, are far better at boosting comfort than things like simple wooden chairs. Relaxing on a bed is another good way to boost comfort, as your sim can day dream or read. Going in the hot tub also boosts the Comfort bar.
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