And this the history and bitcoin table when discovered in the world from 2009.[Using USD Rate 2017]
2009 [Discovered] - 1btc = $0
2010 - 1btc = $0.1 - $0.08
2011 - 1btc = $0.75
2012 - 1btc = $9.04
2013 - 1btc = $301.20
2014 - 1btc = $753.01
2015 - 1btc = $451.81
2016 - 1btc = $828.31
2017 - 1btc = $3664.25
From this list we know bitcoin is not stable , frequently make increase and reduction on price.
Is there a possibility of a decline in the price of the bitcoin future , in doing so we must make a choice better invest a bitcoin or not ?
In fact there is! On July 2017, you did not include the fork that just happened which significantly reduced the rice of bitcoins down to $1950. Also, the price of bitcoins also decreased recently like 2-3 weeks ago due to China's banning of ICOs in their country. There are many factors that affect the price of bitcoins and due to its volatility, it is also very hard to predict whether there may be an increase or decrease on the short-term perspective. But the chart you provided is very accurate towards the increasing part of its price. Even though there are factors that decrease its price, it still remains that in the long-run perspective, the price of bitcoins still increase.
Yeah that information is not very accurate and doesn't represent the extreme polar growth of Bitcoin in both exponential rises and crashes. It makes it seem like the price was stable at those rates when it definitely is not the case.