We have all been told that we should only trade with money we can afford to lose.  This does not mean to be wild and care free with your trading money. So we do not want to think of our trading account as money you can afford to lose. We just have to know that we can lose this money and not affect our life style.  You want to be stingy with this money and try to keep it and guard it with all the skill we have.
Playing offence is important but you will keep and make more money by playing defense with your money.   Before making a trade you should always think defense and check the risk before you place the trade. Once you have the risk figured out and you are willing to accept that level of risk you need to figure out the number of lots you will trade.   It is best to think about how much you will lose rather than how much you will gain. When you approach trading defensively first, then money management will have a higher priority in your trading decisions.
If some news is coming out and you cannot control the outcome then the extra risk may not be worth taking the trade. If you are not sure what the risk is, then it is better not to take the trade because you are increasing your chances for a loss if you do take the trade.