I heard that investing in bitcoin is dangerous. How true is this? 
Investing a huge amount of cryptocurrency is very risky depending on how in depth your knowledge about the flow of market. There are investors today who are suffering a huge amount of investment loss because they tend to sell their coins even at the lowest price when there's a huge down time in the market.
it doesnt matter whether you invest huge or small amount because they are still both risky. any invest is always risky and not just on cryptocurency . we do always need the risk in order to earn but if your only sticking on your comfort zone and not taking any risk , then you cannot possibly improve or become succesful in life. overall investing in bitcoin thesedays is still recomended because bitcoin has not yet reach its full peak.