Every trial in the F.LD.I.L is unique in some way, but that doesn't always mean that 'passing' the trial is the end.
Life itself is, at its core, a constant repetition of trials. For mortals with a limited lifespan, their trials may include finding enough food to eat for the day or looking for a significant other to start a family with.
Of course, there are many other things that ordinary people must overcome if they want to live a successful life until their eventual death.
Cultivators, on the other hand, especially ones with higher cultivation, have their own set of difficulties that they must overcome.
One of those difficulties is time itself. More specifically, going into seclusion for thousands, hundreds of thousands, or even millions of years if you're strong enough.