I've trained or known 100's of traders over 31 yrs and every single one me included had huge almost career ending loses going short at one time or another . Seriously no novice trader should ever go short and most seasoned traders should not be shorting more than 10-20% of their trades short . Imho on what i've seen over 3 decades .
Funny you mention this. The only time in 21 years i got a margin call was from shorting JNPR before earnings.