Although you are right, we have to remember that the formula is the same in trading and investing. That is, invest and trade with the amount of money you can afford to lose. Only when you are able to lose the amount of money will your energy and inclination towards investment work, but you will not be emotional. Many times it is seen that people are afraid of investing, but instead of being afraid of investing, they participate in the investment with the money that they can afford to lose.
What you really mean is that both investing and trading involve risk. Those who are going to invest or trade should invest with risk because sometimes you can make money from investment and other time you can lose your money from investment. So invest as much as you can afford to lose.
For example, if you can afford to invest $10, you can invest from here if you are not emotional about losing it. Never invest by force but invest as much money as you can afford to throw away, you may make a lot of profit at one time and may also lose. You should invest only the amount of money that you can afford from your point of view consistently, or else you will force yourself to never invest. However, if you are investing for long term then it must be sustained and once you can get huge profit from it then hold it.
To be successful in investing you must first control your emotions. As per your example, let's say you bought a coin worth ten dollars, a few days or a week after the purchase you saw the price of that token or coin dropped, then you sold your coin on impulse even though you thought that the price of this coin might go up. If not, then none of your investmentNo value left.So you should plan your investment in such a way that even if you suffer temporary losses, you will be able to hold it patiently for a long time.
Yes it's good that one should plan before investing against temporary loss because the market is not a stable one, but one thing any investor must note is buying the real coin not all coin in the market is worth investing and holding or exercise patient when it's dropping that is why it most advisable here to only invest on BTC even if one seek to diversify it should be a coin that is having some marketing stability , because many coin is pump in day in day out and virtually all is no where to be found in the market investing on such and holding with hope of future rise can course you serious pain that can't be cure the best is to take the little this left when the market is falling most if the investment is coin that can't withstand the market force after being pump. But if the investment is on BTC one don't need to border as long you can hold for long term and keep accumulating with the strategy mostly the DCA you will still recover the drop in the market.