That was true enough. In some Naruto fanfics, Hatake Sakumo was often described as a ninja who had never failed a mission, but Sarutobi Toru knew very well that in this world, no ninja could guarantee a mission's completion one hundred percent of the time.
And it was not merely a matter of strength. Sometimes, it depended even more on luck.
For example, Sarutobi Toru had once received a mission to retrieve intelligence from an intelligence outpost in a certain town. By the time he arrived, however, the entire outpost had already been wiped out. It was also covered in Explosive Tag traps. If he had not escaped quickly with the Flying Thunder God Technique, he might have died there himself.
At the speed Sarutobi Toru had possessed with the Flying Thunder God Technique back then, it had only taken him a little over ten minutes to get there. Yet in reality, that intelligence outpost had been eliminated a full day earlier. In such a situation, no matter how capable you were, unless you could turn back time, it was impossible to truly complete the mission.
Every Jōnin who had carried out missions for several years had basically encountered this sort of trap-filled assignment. If you ran into one, all you could do was count yourself unlucky.
If there really was a ninja who could complete missions one hundred percent of the time, then unless it was just their village deliberately boasting, they were either a Genin who had only graduated a year or two ago and had barely done any missions, or an absurdly lucky bastard who could win the lottery three times in a row.
Hatake Sakumo was naturally no such lucky bastard. His luck could not be called bad, but it certainly was not the sort blessed