Many people think that bitcoin should move up in a straight line but this is not how the market works. Markets may show us many up and down before moving up and sadly people are not ready for these movements and sell their bitcoin before it reaches the all time high.
The truth is most people who do sell bitcoin at a loss see it as a get rich scheme and they don't expect it to lose like 20% of it's value, so if the price dips they'll listen to FUD and panic sell.
Only true enthusiast will hold BTC no matter the price because they know the true value of Bitcoin and that will not make them panic when the price dips.