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.
Who are those people ? because those who knows about crypto does not have that belief instead we knew that line is going Here and there.What I'm saying here is that straight line will never happen until time comes that Crypto will be accepted by the whole world.
that is the reality of life and we cannot just pretend there is a straight value when there is nothing we can do about it.
As you said, a straight line can never be expected, so the investment must be done aiming long term returns. For this reason, patience and cold blood are needed during the bearish times.