Many people who have held bitcoin for a long time have been through several boom and bust cycles. Recently, many folks have noticed a pattern to these cycles linked to the bitcoin halving event that happens every 210,000 blocks or approximately every four years. The next one is anticipated to occur in April/May 2020. Historically, these halving events have not been properly priced into the market, thus causing a large bull run; followed by a bear market. This bullishness is supported through fundamental factors that cause a downward shift in the supply of bitcoin while historically, there is a possibility of an increasing demand for it. If this is true, this ultimately could lead to a price surge and eventually correct back to a new equilibrium price.
https://medium.com/coinmonks/the-bitcoin-squeeze-95c2ea30d725
