I actually felt like I was part of the team and making the product a reality. I was a founding engineer, employee #1. I out lasted every other founding member including the co-founder. I ended up picking up his slack.
Four years and lots of revenue later I was let go. Apparently I "outgrew" the team, what the fuck ever that means. Lesson learned, think of yourself first. A business is just a business and will get rid of you as soon as it can, so you do the same.
My second mistake was working too much. I didn't value my own time and should have spent more time with my family instead of slaving away for someone else's idea. Lesson learned, put you and those important to you first. A job is just a job, a company is just a company. None of that is worth losing time with people that actually matter.
My third mistake? I didn't make any more :)