You just haven't found the right strain yet, bro... is a phrase used the satirize the condescending and missionary position of cannabis enthusiasts who think cannabis is the drug for everyone. There are variations on it, and the real life approach might be a bit more subtle, but the basic idea of pushy marijuana users is a real thing.
First, a little bit of the real science behind this. Cannabis contains dozens, if not hundreds, of different psychoactive chemicals, all with different effects. There are also two major species in the Cannabis genus: Cannabis indica and Cannabis sativa. These species typically have different concentrations of the main substances, with Cannabis indica varieties having more of the sedating, anti-inflammatory and relatively less psychedelic CBDs, while Cannabis sativa varieties are higher in the stimulating and psychedelic THC. But that is the most basic of thumbnail sketches. In addition, especially since the legalization of cannabis, growers have worked on creating a number of different varieties, all with slightly different profiles.
But even though cannabis does have different effects, and people adjust to it differently depending on conditions, cannabis is not for everyone. For some people, cannabis is liberating. For others, it is a fun diversion. And for others, it is somewhere on the scale of problematic to unpleasant. And there is a class of cannabis users who identify with the substance so much, that they refuse to acknowledge this, and say that users just have to find the right strain, or maybe look at the right stars and/or flowers, and all the complicated psychological and pharmaceutical effects will float away into bliss.
It is interesting to me personally because I have been around cannabis all my life, was an occasional user, and have always supported its legalization and social acceptance. I think it does good for most people. But in the past few years, my experience has slid from "fun" to "anxious", and I no longer like to use it. And it isn't because I am either ignorant of cannabis, or closed-minded and just need to find the right strain and relax. It doesn't work for me anymore. And I have come across people who won't accept that.