Jesus reacts to Peter with expletives undeleted. I won't speculate on what the best translation of that might be, but it has something to do with what's behind. Jesus makes it even worse. If any want to become my followers, let them deny themselves and take up their cross and follow me. Nobody wants to hear that.
Nobody wants to preach that.
But it's God's truth as Jesus told it. He has to say it three times in Mark to get it across, and frankly, I'm not sure most of us have heard it yet. Self-denial and sacrifice. Persecution and a cross. The same mortal woes every human being faces plus a few more.