The dotted lines mark past halving dates as well as the projected 2020 and 2024 halving dates.
Bitcoin market cycles have corresponded to each halving. Since the advent of Bitcoin , all Bitcoin halving dates have been followed by bull markets, which are then followed by a bear market and accumulation periods. Given the current long-term trend of Bitcoin's lifetime market patterns, each bull market should be less extensive than the previous bull market. That being said, patterns can always be broken, and this cycle is no exception, regardless of its longevity.
I do not hold any Bitcoin at the time of writing (June 5th, 2019).
Do your own research.