Basically this and a lack of discipline to keep following through on it when I started.
I'm in a good spot now because I have tip money coming in, so I save most of that, back then it was impossible to save when I was making $8 an hour and only working 12 hours.
But what blew my mind was that I've been working for this company for the last three years and they don't have a company backed retirement plan. I just signed up for a Roth IRA because I don't want to be having to work at the age of 75 like people I work with.