just take bitcoin for passive income, dont take it for full time job.
because bitcoin is unstable and you must have job to rely on.  

May be I will quit my job in future if the value of bitcoin reaches to the moon, or may be will get full time on it after 5 years, as after 5 years we will have an clear picture about the future of bitcoin.

with methods and a good strategy and skills in terms of trade you can get monthly cash faster. evem you can earn per day.
even my friend could get his profit of more than 1 BTC for each sale their coin.  great! my friend doing trade altcoin

Dealing with trading we are dealing with lucky and well to be honest i doubt when the bills come to pay the lucky can pay them,without a fixed income isnt the right option to left any work.Sure your friend were able to make a good profit but how much did he invested?And maybe he made some goods investments ,but in the road he had lost as well.

I don't think I'll quit my current job, because my earning from bitcoin isn't fixed. I earned a way more from my job than bitcoin.

it all depends on our ability to obtain bitcoin more. some of my friends have been out of a job and chose to focus on bitcoin, even they can get results 3-5 times higher than their previous work

Truly if someone has the ability to earn 2bitcoins a month, then he can have a good living even if he quits day job which is only possible in few exceptions like users who do freelance jobs.

Exactly, that's why it's not safe to quit the daily job to go full time with bitcoin, it's a little risky method. In addition i think working with bitcoin don't need really going full time, you can working in it with your partial time

It means you rely on bitcoin alone to to finance your daily needs. It does not have to be from trading. The income can come from any thing that involves bitcoin. If you do not have a steady income from bitcoin, then it really is risky. But if you do, it can be a good.substitute to your day job.