We didn't know what to do, so we did nothing/ were doing nothing [closed]
Solution 1:
My spouse (German speaker originally) constantly makes this mistake.
When you say, "I was writing a letter," that is an incomplete thought. Whenever my spouse makes a pronouncement like this, I ask, "When the storm hit?" Think of the past progressive tense as painting a picture, a backdrop, that will make the plot development be more meaningful.
You can also use the past progressive in a nostalgic way. But there would still be some context, for example, "When I was little, I loved to make mudpies. When my mother was gardening on her day off, I was having fun with dirt and water too, but in my own way."
Tenses of verbs are used to make sentences, but sentences also have a context. We don't need to use the past progressive unless there is some appropriate context.
You could check if English Language Learners has a more complete answer.