I know how you feel.
Rarely, if ever, do two people experiencing the same moment together experience it the same way. Ask anyone who has gone on a first date. So, to hear someone say, I know how you feel causes instant skepticism in my mind.
For example, I have several dear friends with special needs children. I also have a special needs child. But, each one of those children is unique. My experiences parenting my 6'6" son with ASD will be different from my friend who experiences parenting her nonverbal son with Downs Syndrome.
Siblings also experience childhood differently from one another. My father is the youngest of eleven. At no time did all eleven live in the same home at the same time because the oldest was eighteen and married and the second born was going to school out-of-state when my father was born. The family can be broken into three generations. Older siblings cared for younger siblings. The older siblings cannot remember a time when there wasn't another child living at home. My dad had two years alone with his parents. If you ask him, he will tell you that is one of his most cherished times.
Now consider the disciples. Each of them--though arguably not with special needs--had their own quirks. Peter and John, as oldest and youngest, spanned at least a generation if not more. Each disciple had his own experience with Jesus, his own take.
Yet, within the four gospels, we have a definitive, inspired, corroborated account of Christ's life.
We need all four accounts because without them we would only get a one-sided view. We require Matthew's recount of the Sermon on the Mount with its focus on law and grace. We need the awe, God-fearing tone of Mark's gospel, traditionally Peter's retelling. We find confirmation in the miracles as emphasized by Luke, a physician who traveled with the thirteenth apostle, Paul, who saw Jesus on the Road to Dasmascus. We fall in love with Jesus through John's personal story.
Of all the disciples, John lived the longest. In many ways, he had the most time on earth to live with Jesus' presence--both as Incarnate Christ and indwelling Holy Spirit. It doesn't invalidate the other gospels by any means, but it places an eyewitness in every scene. John, who leaned against the chest of Jesus, writes with the rhythm of the Savior's heart.
But, we cannot say to John, I know how you feel, because we did not not stand at the foot of the cross.
Yet, because the disciples obediently recorded their experiences, we can come to know what they know. We can receive and believe the greatest love story ever told.