Moses didn’t want the ‘job’ in the first place. At the end of a long exchange that reflected Moses’s reluctance we read …
EXODUS 4:13 But he said, “O my Lord, please send by the hand of whomever else You may send.”
Then having to endure years in the wilderness with this ‘stiff necked people’, and multiple issues, including numerous examples of the people murmuring against Moses….
EXODUS 17:3 And the people thirsted there for water, and the people complained against Moses
But worse we’re those moments when they wanted to stone Moses.
EXODUS 17:4 So Moses cried out to the Lord, saying, “What shall I do with this people? They are almost ready to stone me!”
Moses wasn’t a ‘super human’. He was listed as being ‘meek’, so maybe had ‘super human tolerance’? But even that would arguably have limits.
Either way, this ‘reverting back into his flesh’ and reacting ‘in the flesh’ was costly! (unfortunately) They were at this time ‘under Law’ - and in this ‘moment’ Moses violated the first commandment - and because they were in the wilderness, Moses had to die - this being the (only possible) penalty. Some would argue that Satan ‘incites the flesh’ - as he did with David, inciting David to number Israel - and that could well be argued to have happened with Moses.
As Paul says in Romans, the Law ‘incites’ the flesh. The Law provokes ‘sin’. That’s what ‘got through’ to Moses. The first time Moses ‘struck’ a Rock (to produce water), they were not yet under the Law. The difference here is ‘the Law’.
The point being, the ‘flesh’ can not keep the Law. True for even the best.