do their best to get it right is better,no one is a machine,even the most experienced professional performer can slip up.
An item can be performed competently [no errors]but be lacking in passion and emotion. another song can be performed with the occassional slip but still be more exciting.
of course I advocate that everyone should try and be as professional as they can[ but it is not the oNly ingredient to a successful performance]
AS A PROFESSIONAL I Spend several hours a day, practising, singing and playing, but I can still mess up, the same as everyone else. Dick Miles