How do I carry the weight of designing devices lives depend on?

You imagine every way your device could fail because you know a life sits on the other side of it. That care is exactly why you are trusted with this. But carrying every failure mode alone, all the time, is more than one person is built to hold. The imagining is your gift and your burden. It makes your work safe. It also means your mind never fully sets the work down. You have to separate the vigilance the job needs from the dread that follows you home, because they are not the same thing. Write the failure modes down and let the document hold them, not your body. When a worry surfaces after hours, note whether it is already on the list. If it is, you have done your part. Trust the record so your mind can rest.