It is absolutely true for newbies because trade on emotion is very harmful because if any one trade with emotion they will fall in loss. When we go for trade then we need to buy at low price and selling at higher price. But when emotion works then sometimes we may observe that when price go up then emotionally we go for buying and when price go down then we go for selling. It occur by emotion.
You're right, don't do anything in a situation where you're in a high emotional state because it's clear that his way of thinking leads to mistake after mistake. especially clear is that when trading sometimes we feel that this will continue to increase with full confidence and feel right but not knowing the situation immediately changes and does not achieve what we want, because the emotions of wanting to achieve the greatest value and not receiving the profit that should have been quite acceptable.
Actually, everyone will experience this, not only beginners, even those who have experience, this can happen but usually people who can control themselves because they have experienced this and don't want it to happen again, once again experience is the best key.