I just want to know that why I can't use "very" in this sentence instead of "so":
"She became very frustrated with the lack of feedback from her boss that she decided to look for another job."
In my opinion, "so" and "very" both have the same meaning, don't they?
Your quoted sentence doesn't make sense.
If you write
- He became very frustrated that his boss appraised him wrongly and it affected his career.
It would make sense, and it would mean "Because of his boss's wrong appraisal his career is being affected. And that's why he is frustrated."
So...that is a set expression.
Example -
- He became so frustrated that he started to look for a new job.
Now consider sentence 1 and sentence 2. While sentence 1 states the reason of your frustration, sentence 2 states what you did because of it.
Places where so can be replaced by very
- He is so/very angry about the way the event unfolded.
Your sentence -
She became so frustrated with the lack of feedback from her boss that she decided to look for another job.
What is the cause of her frustration - The lack of feedback from her boss.
And effect - She decided to look for another job.
in that sentense so indicates a personal opinion. it is more wishy washy. whereas very is more clear and straight forward. you can use either one depending when and where you want to say it.
Usually, very tells us "to a significant extent/degree" (in the opinion of the speaker).
On the other hand, so tells us "to such an extent/degree", and originally meant something like "in this manner". When used as you did ("She became so frustrated..."), there's usually a following phrase with "that" (a subordinate clause) explaining the extent.
A good example is a common joke you can sometimes hear on TV or comedy routines. Someone says "My brother is so stupid." and the audience yells "How stupid is he??". The joke finishes "He's so stupid that he showed his ID when he bought root beer.".
Sometimes so may be used in a phrase such as "That wasn't so hard.", again meaning "to such an extent". The meaning is like "That wasn't as hard as you thought.".
In modern speech people often say things like "I'm so tired." to mean "I'm very tired.", but there's a feeling of an unspoken situation which could be true because of how tired the speaker is, as in "I'm so tired that I could sleep while riding a roller coaster.".
