This sentence was crazy!
Any mission!
One had to know that when a mission was given, sometimes it might be a spy mission.
For example, Yun Jian and his group disguised themselves as ordinary people and hid around the target as spies. A normal spy would need a few years of incubation period.
They also needed to gain the trust of the target. In the end, when the target completely relaxed his vigilance and treated him as someone that the other party trusted, he would take the opportunity to catch the other party’s weakness and wipe out the other party’s lair.
Assassination was not the only type of mission in this world.
Some missions could see success or failure in a few days, but some missions had incubation periods like AIDS. It would take years or even decades to complete this mission.