Don't expect what happened in the previous cycles to repeat itself that is one rule about Bitcoin. When they mean by increase in the price of Bitcoin it doesn't mean the price will double times 2 every four years. The price could go up a little giving significant profit to those who wish to sell off their Bitcoin.

Expecting a double in price may never happen or it may. No one can fully understand the nature of Bitcoin and where the price is headed in a specific timeframe. We could predict the price to increase to a certain amount in two days or a week (may not be certain still) but what it would be next month, or next year, or in 4-10 years we cannot tell.