The rule is very true. What book is it from?
Dr. Alexander Elder advice for traders.
Very good comments about trading, and life in general. I've always likened trading to other skill based activities. Professional sports always come to mind; developing skills and attributes won't make you a success - all the time. There are others out there trying to beat you, and you might just have a bad day.
And, most of all, you're only as good as your last successful day!