You will not have a decent pay for years. Get used to be broke all the time. That awesome band is playing? Forget about it. Nice clothing? forget it. You will have 20 t-shirts of your startup and that will be your wardrobe for a long time.
You will pay the bills, clean the floor, prepare coffee and be the first to arrive in the office and the last to leave. You will change. You will face fears of losing your skills as designer. You will feel like shit when doing spreadsheets for hours.