To accept investment, you must accept risk   

Any investment is a risk. Nothing is guaranteed, especially in bitcoin. Its value fluctuates. You can monitor its progress but you can't control its market. Therefore, to feel less stress on your part, just invest what you can afford. Or, better yet, invest in ICO. Most start-ups in ICO makes use of crytocurrency in their transactions. Everex, have you heard it? goo.gl/E2NDF2, use bitcoin and ethereum to build a faster and better remittance service.

Joining ICO is also a risk but it's a win-win. You use bitcoin and you also invest money in a start-up that you think can change the world for the better. 

Bitcoin prices are starting to increase again as users continue to increase over time, and i think there is no risk to invest in bitcoin either short or long term. Even today many investors are lucky in investing in bitcoin

I think there is no guarantee that investment is always profitable, it will hurt if we are not ready with risk, high profit of course high risk, so we must prepare mentally if we get loss.

Well it is risky but not risky enough compared to gambling. Check this chart out: https://www.coindesk.com/price/ - Under that, you can see the history of bitcoin prices and it is worth note taking that the prices actually increase overtime. Compare it to last January 2017, the prices were only around $1000 and right now it has reached up to $3200. In my opinion, the prices could reach up to $4000 by the end of the year but you need to take the risk on investing.

i think that the risk in trading is different from person to person. those people who do not have any experience in trading then they have more risk in trading, as compare to those people who have good experience in trading. but it is also a fact that if we compare bitcoin trading with gambling then gambling is more risky, because there we totally depending on our luck, while in trading we can use our skill and experience.

Bitcoin investment is not free from risk.It is a decentralized currency uncontrolled by any authority and so its price is highly volatile.Its price either increases or decreases with variation in demand for bitcoins.But if we see the previous price history of bitcoins,we could see its price has increased from time to time in a long term basis.So,investment could be made in bitcoins with full confidence.

Any kind of high-profit investment is of course high risk, and we all know that bitcoin is decentralized so that no person or group can withhold the price, everything is pure from the market.

Yes, that is definitely right, putting your money into "investment" is always taking all of it into risk because who knows when will it pump and dump especially we cannot predict what will happen the next day to our investment so it is a 100% risk totally. But if you are old in this field, you analysis skills  will increase over time and in the long run you will mostly earn profits.

All types of investments are at risk of value volatility.
When Bitcoin is new to most people, they do not know the future potential in it, but what they do is to think positive because this is widely recognized and accepted cryptocurrency by huge companies for payments and remittance. few years past Bitcoin valued a hundred of US dollar but now a few years after BTC is equal to $3k. So I can say, Bitcoin has the potential to replace monetary currency in our pockets.