Those who basically spend 80 percent of their income on basic family expenses. If they start investing without creating an emergency fund and suddenly their expenses increase and they fall into a financial crisis or disaster, they will not be able to maintain their investment.
People's income and expenditure are not fixed. Some people have much less expenditure than their income and some have much more expenditure than their income. However, normally those who have a discreet source of income may have an expenditure of 70-80 percent of their total income. The money left after expenditure is basically discreet money which is needed for investment.
Now, there is no need to deposit this discreet money in the emergency fund at the beginning, especially for investment. Because your investment fund has not become valuable yet. So there is no need to pay much attention to the emergency fund at the beginning, rather you try to pay attention to investment at the beginning. Emergency fund becomes important for you after starting investment. If your discreet income is very high, then you can also focus on building an emergency fund along with investment. Remember, there is not much need to buy rope before buying a cow. So delaying investment to build an emergency fund will not be the right thing to do.