Is there a good "rule" about when to use an article? Some solutions require "A" or "The" while others do not, and I cannot see a pattern. A literal translation. "The surprise is a big factor" was marked incorrect, whereas in another example, leaving it out was incorrect.
"Surprise" is an abstract noun, so we wouldn't use "the" here. However I (wrongly) lost a heart a couple of lessons back for not putting "the" before "growth" on its own.
Abstract nouns only normally take "the" when they are qualified in some ways - "the growth we have experienced recently". But I can't think of one for "surprise".
I really think "The surprise is big/great factor" should be accepted. What if you are talking about a specific thing that will cause a surprise and the aforementioned surprise is a big factor in why or why not to do it?