There are two kinds of Missions. Or missions belonging to two time frames: finite and infinite. I believe you are writing about finite missions - and of course they do fail or are completed.

Purpose can be finite and infinite too. Infinite purpose belongs to an aim and not a goal. Goals can support an aim, but aims do not support goals.

Your use of purpose here frees it from the finite world of goals, or of winning or losing. Purpose from the infinite does one other thing besides making it infinite - it makes purpose as self-fulfilling prophesy. Once that happens then play becomes the aim of the purpose where many goals spring out.

As a healer my mission or purpose is to reveal suffering. Until we evolve to a very high vibration as a species where we learn the values of suffering and embrace it, my purpose falls into an infinite mode. over many lifetimes (IMO).