People often ask the question, "Why must we suffer?" Philosophers and many others have been debating that same question for ages. Even in the pre-earth life, I believe the question was raised. If I may interject some opinion, I think that Lucifer learned about the Plan of Salvation and was scared. He did not want to suffer, which is one reason he wanted all people to be forced to return to live with Heavenly Father (although, on the other hand, he knew his plan would not allow anyone to return to live with God). He thought that would prevent suffering. He also was prideful, he wanted Father's glory and power without expending any of the effort. He wanted that glory regardless of what it would cost others. He may not have fully understood the Plan but I think he did. I think he understood it and was scared. He was afraid of the suffering - of the pain and sickness and sorrow.
There have always been some who were scared of suffering and sought to eliminate all suffering, regardless of what it might cost. Others sought to understand suffering and did not shy away. Even though philosophers have argued over the meaning of suffering for millennia, truth about it comes from prophets.
Lehi, speaking to his son Jacob, "Thou knowest the greatness of God; and he shall consecrate thine afflictions for thy gain." (2 Ne. 2:2). "For it must needs be, that there is an opposition in all things. If not so...righteousness could not be brought to pass, neither wickedness, neither holiness nor misery [note the interesting and important juxtaposition of those two], neither good nor bad." (2 Ne. 2:11). Why are misery and holiness placed in opposition? Holiness is consecration; it is purity and sanctification. Does that mean that there is no sadness for one who is holy? No, but is means there is no misery, no being miserable. The distinction is important. It does not mean that those who are miserable have necessarily sinned, although "wickedness never was happiness" (Alma 41:10). However, sin will always bring misery.