You become a jack of all trades, master of none. Most days you're stretched so thin, working on various projects that are far above your skillset that you can only hope to be floating above water because most days you will feel like you're drowning. If you make any type of mistake or do something that is not to the owner's insane standards, be ready to get berated at high frequencies and to be threatened with no pay or reduced salary.
Expect to work 10-12+ hours a day and work on the weekends. Easily the worst job in my entire career (surprise, surprise ZERO retention rate here!)