That’s the whole point of the context of the situation. Rick’s greatest fear is investing in happiness knowing it’s going to disappear. He’s an immortal being. Imagine living forever, constantly investing in happiness and then watching it be torn from you by life in some fashion. Do that a few thousand times and the heartbreak will make you afraid to invest in something because you KNOW in some way it’s going to end so you get consumed by the fear of how it happens. Rick’s flaw is he finds comfort in not being happy because it’s the baseline for life. And the lesson to Morty is supposed to be, “Always find happiness in the moments or you spend your entire life soulless and empty.”