Just as jokes get lost in translation, tone is easy to misconstrue without the context you'd get from vocal cues and facial expressions. Accordingly, it's easy to come off as more abrupt that you might have intended — you meant "straightforward," they read "angry and curt."
To avoid misunderstandings, Pachter recommends you read your message out loud before hitting send. "If it sounds harsh to you, it will sound harsh to the reader," she says.
For best results, avoid using unequivocally negative words ("failure," "wrong," or "neglected"), and always say "please" and "thank you."