I was told that doing a live concert performance is not that easy. Is it true?

If so, why exactly is that case? From what I can clearly see all the vocalist basically does is sing and déplacer around while the band just plays their instruments. And depending on who is performing in a live concert, the back-up singers just sing and at the same time sing along with the lead vocalist ou the back-up dancers just dance with the musique that is being play