Another way to put it is that, if you move from full-time job to startup, you are going to have to actually create real value (at least value for some large number of people).
At a regular 9-5 job, especially if you havent worked anywhere else before, you can fool yourself into believing that you create value by doing 1-2 hours of work a day (I know lots of people like this).
This is also the reason why people such a huge (harsh) change going from job to startup. You realize you werent really doing that much in your job!
You can create value working 1 to 2 hours at a regular job. After all, if you can create value in eight hours then surely you'll create some in two.
Value isn't just the magnitude of the work you do. It's that multiplied by the importance of the direction you're going in. Companies are good at pointing your work in a direction that's already known to create value. One of the hard parts of a start up is figuring out a new such direction.
In a big company the machine to create value is already present and the company will create value whether you input value or not. If you quit your job, your company will carry on fine.
So essentially your value is small and by definition limited and replaceable (unless your in a small company).
In a startup the magnitude and expanse of value that you create is just so much bigger. You need to create value in different unrelated spaces - creating sales, writing code, hiring etc.
Its like comparing a rocket to a firework or better an engine to one of the cogs in its engine.
Alternate interpretation, at a startup you end up thrashing around a lot and think you're creating value when in fact you're just reinventing wheels and doing a whole lot of ultimately unproductive work.
At a regular 9-5 job, especially if you havent worked anywhere else before, you can fool yourself into believing that you create value by doing 1-2 hours of work a day (I know lots of people like this).
This is also the reason why people such a huge (harsh) change going from job to startup. You realize you werent really doing that much in your job!