As you said, it is like trying to swim without a life jacket, basically we put on a life jacket before we get into the water. But if we use this in the case of investing, it will not be right at all. If we wait to build an emergency fund before investing, it will not be the right approach at all. You can build an emergency fund along with investing. This will keep your investments running and your emergency fund will be built. For example, you can build an emergency fund with 50% of the amount you are willing to invest and invest with 50%. In this way, you will not miss out on buying opportunities and you will be much ahead of your portfolio goals. It will be good to build an emergency fund along with investing.
I see your point. It's a balanced approach between earning money and saving for emergency. But i think a person should have an aim of securing basic emergency fund before investing so that in future he can not be forced by the situations to sell off his investments in case of an emergency. Even a few months of saving for an emergency fund before investing can help one in not selling his investments. While your 50/50 approach can be beneficial I think it's more suitable for those who have stable income and higher risk tolerance.