Apparently, from the way he has placed gambling, I am sure even if he decides to come back to gambling, it is not like he still won’t be able to control himself. What he has done basically is to be in control, and that can only happen when you have the right mindset towards gambling and this is totally different when it comes to those who are addicted. People with the wrong mindset of trying to get rich from gambling and usually the ones that will not even find it easy at all to be making decisions like this.

My friend decided to sell his car and invest all the money in Bitcoin as some people predict that 1 BTC will reach 500 000$ till the end of 2019.
He totally believes in it and tells that then he could buy not only a new car but a flat also.

Does it really worth it? He uses his car for his work and now he wouldn't be able to do this anymore as he thinks there's no need to work anymore.

I also believe this is true, but the problem is gambling is a form of competition, and humans will always be competitive. Whilst there is one human who thinks he is better than another, a gambling type circumstance will always form. e.g. I bet you I can do this, and you can't. It's only natural that systems form around this trait to make it easier to wager.

it's really important that we all have to stay patient waiting for the market back up again as before, because in this month same month last month the market experienced an unimaginable decline. but with the time is not long certainly the market will be back in the original

As we can see now everyone/every developed nation is moving towards digital currency. In your opinion how much time is required for digital currency to take over the current/existing market or it is impossible that digitisation will never be successful. If yes what are those factors ? In my opinion those countries which are not accepting digital currency, are doing wrong. They are only thinking about the tax. They are saying that we will not get any tax and digital currencies are fake. Fraud is very easy in digital world (that is true but it also happen in every market). Although when someone is doing business in digital currency then that person is bringing money to country that is beneficial for the country...

That's just predictive , no one can know exactly how  the bitcoin price will be in the future because bitcoin is always influenced by many factors. But in the future, I believe the bitcoin price will be much higher than in 2017 because the cryptocurrency market is still a new market and it is attracting a lot of investors and big companies, besides bitcoin is believed to be a bubble and it will explode when its price is really high .

I stop gambling when I win a lot of money because I know that if I continue I will lose not only the winning but also my own money. Therefore it is best to quit gambling atone when you realize that now you have made handsome money. There are other days to come. You can gamble more on other day but don’t continue on the same day.

That is a good advise, gambling is not really a helpful activity when we are talking of earning money.
It's actually wasting money because you do not win all the time, or even most of the time, they have the house edge so you have to pay to enjoy.

you should not be too regretful, take advantage of the existing situation, when the cheap price always try to buy coin and sell when the price is green and when it is getting the benefits and better you control your patience.