How do I choose between my people's welfare and the mission?

You carry two loyalties that usually run together and sometimes tear apart: the people under you, and the mission you are all there to accomplish. When they pull in opposite directions, the weight lands squarely on you. That is one of the hardest things leadership asks, and feeling torn by it is the mark of a leader who actually cares. Most of the time the choice is not as total as it feels in the moment. Taking care of your people usually serves the mission, because people who are cared for and led well perform better and endure more. The rare, real conflicts are when the mission genuinely demands a cost from them. Then your job is to be clear-eyed: is this cost truly necessary, or am I spending them for something that does not require it? When the two split, protect your people from every cost the mission does not truly require, and be honest with them about the ones it does. Do not dress up a hard call as an easy one. People can carry a great deal when they trust that the person leading them would never spend them carelessly. Earn that trust, and you will not have to choose alone.