They may also have not trusted that God's provision was enough, and fell into Satan's temptation that they needed to consume more than what God had provided as their appointed food.
That's not bad at all . . . actually.
But why did Adam and Eve sin? To understand this, we need to know what Human Nature is. But wait, there are three Natures mentioned in the Bible: 1. The Sinful Nature 2. The Divine Nature 3. The Human Nature.
Human beings began in the Garden with their Human Nature only. When they sinned, the Sinful Nature was added to their Human Nature. When a person comes to Christ, the Sinful Nature is cut out (Col 2:9-15) and it is replaced by the Divine Nature (2 Pet 1:4).
So . . . what is the definition of Human Nature? Servant. A human with its Human Nature by itself is designed or created, to serve. What will it serve? Whatever comes along and tells it what to do. This human does not have the Guiding Holy Spirit to direct him or her in their ways. They do not have that internal "voice" to tell them what to do. And prior to their fall, of course, they did not have the Sinful Nature.
When the Devil came along, Adam and Eve were ready to serve. For if they were created to serve, why would they not serve Satan . . . doing what he tells them what to do? And that is precisely what happened. Without internal leadership from God, Adam and Eve did what Satan had told them to do. As a result, God Cursed all of the physical world . . . thus death and decay come to ALL things.
The remedy as per Holy Plan? The Tree of Life. Genesis 3:22-24 tells us that to remedy this Curse, Adam and Eve could have eaten from the Tree of Life, but God refused to allow that to happen, for the Tree of Life in the Garden is a pre-image of Christ on the Cross, and like the First Book of Adam and Eve states over and over, humanity would have to wait 5,500 years to be able to eat the fruit from that Holy Tree. And that Tree is Christ, as clearly described in the Book of Revelation.
Eating from the Tree of Life is the act of receiving Christ's Spiritual Circumcision, as clearly described in Colossians 2:9-15. Once that Curse is lifted from an individual Heart, that person will have been enabled to understand, believe, turn, and obey. This Romans 12:2v transformation takes place in a person's life because the Sinful Nature has been cut out and replaced by the Divine Nature . . . but the Human Nature never leaves, for that is the "engine" that causes a person to obey the new Divine Nature that accompanies the Human Nature.
We would all do well to learn about Human Nature and how vastly different it is from the Divine and Sinful Natures. They are all intertwined, and knowing them fully will help to unravel the Mystery of God's Holy Word.