If man started out sinless, then how did sin?

Isaiah 14:12-14 says: "How art thou fallen from heaven, O Lucifer, son of the morning! how art thou cut down to the ground, which didst weaken the nations! For thou has said in thine heart, I will ascend into heaven, I will exalt my throne above the stars of God: I will sit also upon the mount of the congregation, in the sides of the north: I will ascend above the heights of the clouds; I will be like the most High." The prideful "I will" attitude gave birth to sin. Ezekiel describes the anointed cherub's former glory in chapter 28:13-15: "Thou hast been in Eden the garden of God; every precious stone was thy covering, the sardius, topaz, and the diamond, the beryl, the onyx, and the jasper, the sapphire, the emerald, and the carbuncle, and gold: the workmanship of thy tabrets and of thy pipes was prepared in thee in the day that thou wast created. Thou art the anointed cherub that covereth; and I have set thee so: thou wast upon the holy mountain of God; thou hast walked up and down in the midst of the stones of fire. Thou wast perfect in thy ways from the day that thou wast created, till iniquity was found in thee." Satan, the anointed cherub, was not deceived, but sin was born with him. Thus, he is outside the realm of salvation.

Verse 12 provides further clarification: "Son of man, take up a lamentation upon the king of Tyrus, and say unto him, Thus saith the Lord GOD; Thou sealest up the sum, full of wisdom, and perfect in beauty" (Ezekiel 28:12). This is addressed to the king of Tyrus. Is Satan the king of Tyrus? No. But the king of Tyrus is an embodiment of pride, arrogance and selfishness, which are all characteristics of the devil. Sin originated with Satan.

Excerpt from the Book:

119 Most Frequently Asked Questions About Prophecy
by Arno Froese
#1055 - 176 pgs.