What is it about the subjunctive form that makes both native and nonnative users of English intimidated and prone to error ...

The present subjunctive tense is used to express doubt, possibility, requests, and after verbs of emotion. It is also used after certain phrases like 'cuando' and 'para que'.

David Gates of the singing group called “The Bread” started the lyrics of a song with the phrase "If a picture paints a thousand words".