Most learners find Speaking the most challenging of the four language skills: To speak in a foreign language, you need to

• find words quickly enough
• put them in a meaningful order
• not worry about mistakes

For many learners this is a difficult challenge: in your mother tongue, you speak without thinking. At least when writing you have a lot of time to think. 

But the worst thing perhaps is that you speak with someone, and feel embarrassed that they can notice your mistakes. 

Embarrassment, self-consciousness, nervousness... and stress: Stress makes any existing condition more difficult.  For instance in an interview, or talking to someone official: words get mixed up, you can't think straight, your mind goes blank.  

A final year Education Faculty student once told her supervisor one week before her one-month teaching practice "I have problems speaking; when I'm nervous I can't talk at all".  During the previous 3 1/2 years, she had skillfully avoided threatening situations, and no one had noticed the challenge she faced.  But having avoided all the practices that built up fellow classmates gradually to confidence in front of a class, this student was now 'cornered'; to graduate, she needed to teach, for 4 long weeks. 

 Her supervisor asked her to explain the condition, what made it worse and what helped her.  As she talked, she relaxed.  She was less worried about what 'worst possible'might happen: her teacher had listened and been helpful.  

They decided to talk to the class she was going to teach.  The response was positive: most of the pupils were supportive, and kept others in check.  The trainee teacher relaxed, and graduated to become a teacher who could well understand learners who might not find it easy to... do what others did without thinking.