You never know what will happen, but you can be very sure that within a year you're going to encounter a variety of unforeseen financial hits. Not having the money to pay for them leads to stress and sometimes a vicious cycle.
For many Americans, an emergency fund can be an agonizing choice between feeding their family and planning for the future. But for most people reading this forum, an emergency fund it not a challenge once you decide to do it.
Yet for the first couple of years starting a business, I didn't prioritize this. It felt like I was putting more money into growth, but really I slowed myself down as I now and then had to hustle to meet relatively small unforeseen expenses.
After you get an emergency fund, you then ought to think about 3-6 months living expenses in a relatively liquid asset.
After that's done, you can sleep much more soundly.