I am having trouble reconciling the following two quotations:

"[MongoDB is] so simple and natural to use from dynamic languages"

and:

"In my test code, I had an 'async' remove() call (ie. I didn’t wait for it to finish) and was then inserting new entries, and previous remove() happiliy removed them (all of them, or some, or none, depending on the race). Those were very confusing few hours."