Bart D. Ehrman, The New Testament: A Historical Introduction to the Early Christian Writings, sixth edition (OUP, 2016), 163.
When modern readers act as if [the Gospels of Mark and Luke were portraying Jesus in precisely the same way], for example, by thinking that Jesus said all of these things on the cross, some of them recorded by Mark and others by Luke, they take neither account seriously, but rather create their own account, in which Jesus is portrayed as all things at one and the same time. But Mark has one way of portraying Jesus and Luke another, and readers who combine their two portraits form a different Gospel, one that is neither Mark nor Luke.
The Amateur Exegete 