Business owners, what do you wish you knew before starting your business?

The need for your business in your area of work [market, customers e.t.c.].

The cost  / rental of the equipment and premises.

Close by competition / businesses.

For me, it was seasonality. I became a small low end car dealer. I started in like April and by Sept I was doing ok. Not great but I knew I could grow it from there.

What I did not know was from Nov thru March, sales and earnings dropped massively. 

So what I thought I could make every month was only during the good months. In winter, I did not sell much or make much. So it taught me to plan for the lean months.  I earned probably 80% of my earnings  in 7 months.  So I learned not to spend like a drunken sailor just because I had a good July.  But, for the first few years I reinvested easily 70% of my earnings because I needed to be able to afford more cars. And I was not willing to borrow at high rates. (I did it one time early on when I got a package deal on like 5 cars. Back then there were no cash advance fees so I just paid the normal I guess 21%.  I only needed it for about 2 and a half months and I made about 6 times the interest.  But long term I knew I did not need to be paying interest. So I only did it that one time.

That in liberal run cities, my business could get looted and burned down while hearing politicians & celebrities egging the rioters on.