Legends answer.

The objective is for the Sith to survive. Darth Bane recognized that the disciples of the Dark Side will always want more:

"I can't accept what Lord Kaan preaches," he confessed. "He says we are all equals, but if all are equal, then none can be strong."

...

"Do not believe everything Kaan says," she warned, and he could hear the naked ambition in her voice. One to embody the power, the other to crave it. "Once the Jedi are destroyed, many of his followers will discover that some of us are more equal than others."

From Darth Bane: Path of Destruction

So, Darth Bane was aware that the Dark Side would pit it's disciples one again another as they were craving for more power. The problem there was: a lot of weaker Sith would work together to kill a strong one and with that, they'd weaken the Siths.

He was absolutely convinced of this and with that, he indoctrinated his apprentice, which in turn then again indoctrinated it's apprentice with the thought and so on. Plus, having an apprentice gives you power up to the point where you are betrayed. So it is a normal thing to have an apprentice.

Palpatine was not the first to crave for immortality. Darth Plagueis was Sidious master and he already craved immortality. And with becoming nearly immortal, he wouldn't betray the Rule of Two. The objective of the rule is for the Sith to become stronger. If Palpatine had become immortal, always learning more about the Force and becoming more powerful, he'd have fulfilled the ultimate objective of the rule of two: making sure that the Sith survive and grow more powerful.

Legends answer.

The objective is for the Sith to survive. Darth Bane recognized that the disciples of the Dark Side will always want more:

"I can't accept what Lord Kaan preaches," he confessed. "He says we are all equals, but if all are equal, then none can be strong."

...

"Do not believe everything Kaan says," she warned, and he could hear the naked ambition in her voice. One to embody the power, the other to crave it. "Once the Jedi are destroyed, many of his followers will discover that some of us are more equal than others."

From Darth Bane: Path of Destruction

So, Darth Bane was aware that the Dark Side would pit its disciples one again another as they were craving for more power. The problem there was: a lot of weaker Sith would work together to kill a strong one and with that, they'd weaken the Siths.

He was absolutely convinced of this and with that, he indoctrinated his apprentice, who in turn then again indoctrinated their apprentice with the thought and so on. Plus, having an apprentice gives you power up to the point where you are betrayed. So it is a normal thing to have an apprentice.

Palpatine was not the first to crave for immortality. Darth Plagueis was Sidious master and he already craved immortality. And with becoming nearly immortal, he wouldn't betray the Rule of Two. The objective of the rule is for the Sith to become stronger. If Palpatine had become immortal, always learning more about the Force and becoming more powerful, he'd have fulfilled the ultimate objective of the rule of two: making sure that the Sith survive and grow more powerful.

Legends answer.

The objective is for the Sith to survive. Darth Bane recognized that the disciples of the Dark Side will always want more:

"I can't accept what Lord Kaan preaches," he confessed. "He says we are all equals, but if all are equal, then none can be strong."

...

"Do not believe everything Kaan says," she warned, and he could hear the naked ambition in her voice. One to embody the power, the other to crave it. "Once the Jedi are destroyed, many of his followers will discover that some of us are more equal than others."

From Darth Bane: Path of Destruction

So, Darth Bane was aware that the Dark Side would pit it's disciples were craving for more power. The problem there was: a lot of weaker Sith would work together to kill a strong one and with that, they'd weaken the Siths.

He was absolutely convinced of this and with that, he indoctrinated his apprentice, which in turn then again indoctrinated it's apprentice with the thought and so on. Plus, having an apprentice gives you power up to the point where you are betrayed. So it is a normal thing to have an apprentice.

Palpatine was not the first to crave for immortality. Darth Plagueis was Sidious master and he already craved immortality. And with becoming nearly immortal, he wouldn't betray the Rule of Two. The objective of the rule is for the Sith to become stronger. If Palpatine had become immortal, always learning more about the Force and becoming more powerful, he'd have fulfilled the ultimate objective of the rule of two: making sure that the Sith survive and grow more powerful.

Legends answer.

The objective is for the Sith to survive. Darth Bane recognized that the disciples of the Dark Side will always want more:

"I can't accept what Lord Kaan preaches," he confessed. "He says we are all equals, but if all are equal, then none can be strong."

...

"Do not believe everything Kaan says," she warned, and he could hear the naked ambition in her voice. One to embody the power, the other to crave it. "Once the Jedi are destroyed, many of his followers will discover that some of us are more equal than others."

From Darth Bane: Path of Destruction

So, Darth Bane was aware that the Dark Side would pit it's disciples one again another as they were craving for more power. The problem there was: a lot of weaker Sith would work together to kill a strong one and with that, they'd weaken the Siths.

He was absolutely convinced of this and with that, he indoctrinated his apprentice, which in turn then again indoctrinated it's apprentice with the thought and so on. Plus, having an apprentice gives you power up to the point where you are betrayed. So it is a normal thing to have an apprentice.

Palpatine was not the first to crave for immortality. Darth Plagueis was Sidious master and he already craved immortality. And with becoming nearly immortal, he wouldn't betray the Rule of Two. The objective of the rule is for the Sith to become stronger. If Palpatine had become immortal, always learning more about the Force and becoming more powerful, he'd have fulfilled the ultimate objective of the rule of two: making sure that the Sith survive and grow more powerful.