The problem with poker and questions like the one OP poses is this automatically belief that simply because you see someone do it that you can also likewise be just like them...
Grinding poker for an actual income is very stressful, and not everyone can handle that stress. The stress will manifest itself in many ways; not just anxiety or fear but it can translate into impatience, anger, depression, boredom, etc.
Grinding for pennies all day every day can be very taxing.
Sure, its easy now when you break out your spreadsheet and theoretically calculate all the money you can make in a year if you play X number of hands for Y hours for Z days each month...
But the reality isn't near as sexy, in fact, when you do it, you will learn first hand why players call it a "grind".
Here is a thread I've been following of a guy going to school AND has a job AND is trying to grind 5NL and 10NL poker on the side to supplement his income
http://forumserver.twoplustwo.com/17...t-2-a-1321126/
This guy is working his ass off and it is hard freaking work. He started about a year ago and has been grinding 5NL and 10NL and after a year his bankroll went from $200 to around $900.
I feel his struggles are going to be more representative of reality for players like you who are new to poker and think you can just jump in and crush the game and make enough to pay for school and your apartment grinding 5NL and 10NL.
You are in for a rude awakening.
Lastly, you never did give us a background on yourself or tell us how much online poker experience you have (i.e. how many hands have you played and at what limits and when...)