The כלי יקר has an interesting take as to why Moshe Rabbeinu was not allowed to lead עם ישראל into the Land. This is related to Moshe’s being told to hit the rock when they left Egypt. He was told to speak to the rock in the fortieth year of their time in the desert.
The generation that left Egypt were tough. They were used to rough treatment when they were slaves. The generation of the desert, on the other hand, were pampered and spoiled. Everything was done for them. The Manna, the water in the merit of Miriam, and the Clouds of Glory, all made life very easy.
The כלי יקר said that Moshe needed to learn to adjust to this generation. Just like he had to speak to the rock, he needed to approach matters in a more gentle manner. When he failed at the instruction to speak to the rock, he demonstrated he was not up to the task.
Similarly, educators need to adjust to the type of students they have. Sometimes, toughness is required, while at others, kindness and gentleness is what is needed.