Bitcoin's value swings from time to time. To put things in perspective, the average price of a bitcoin in the beginning of 2013 was around $400 per bitcoin, but by the end of the year, the price had risen to over $1000 per bitcoin. This means that if you had two bitcoins valued $800 at the start of 2013 and kept them as an investment, they would have been worth more than $2000 by the end of the year. Because bitcoin's value fluctuates, many people keep them in their wallets.