Warning: what follows is NOT for the attention-challenged!
I am starting with a long aside that leads to A Point I Want To Make:
"Paradigm shifts" is a concept in the general culture now that was identified by an academic named Thomas Kuhn in a 1962 book called "the structure of scientific revolutions." The way Kuhn originally described them, within a science, there's a standing paradigm, or way of looking at something - say, Newton's physics - that over time accumulates "anomalies," things that happen in the world that the paradigm ought to be able to explain, but can't... and then a young Turk type (like Einstein in this case) comes along with a NEW paradigm, and everyone realizes its superiority over the old one, and they adopt the new one.
But Kuhn later realized it isn't nearly that simple. People versed in the older paradigm resist changing, maybe for career purposes, maybe because they just aren't convinced, etc... but eventually the new one wins out anyway, because of a combination of its superior explanatory power and also because the holders of the older one die off and are replaced by a generation that know the new one as the "normal" one.
I like this work because it explains a lot of social phenomena outside the scientific realm. Civil rights in the USA, for example... did they come about because a generation of activists convinced old Southern and Northern racists of the error of their ways? Hell no, but the crackers eventually DIED OFF and were replaced by a younger generation that had grown up with a different sense of what was acceptable...
The other thing that Kuhn had to backtrack on, paradigm shifts aren't "all or nothing," and not necessarily immediate, They can be piecemeal, they can be partial...
So bring this closer to home... HIV and risk and truvada.
I did the reading on that new "Prep" / truvada protocol last year. It sounded pretty convincing as a way to actively prevent transmission of HIV. I have been on truvada for about six months now, though I was never a "big slut about town," I have been known to stick my dick in someone I didn't know, not often, once a year, but still... never even one time bottomed bareback with someone I hadn't known for a long long time, and had tested... but from where I was sitting, this truvada thing looked like a very inexpensive looking insurance policy against HIV, as all I have to pay a co-pay.
Here's where Kuhn comes in... I have been taking the little blue pill every day for six months now, only to realize that I was still not quite ready to take advantage of the safety that all the studies say it offers... those internal paradigm shifts can be slow in the coming... and I doubt I will EVER feel comfortable letting anyone I don't know bareback me.
For a new generation who didn't bury dozens of friends, this med might be part of the "normal" they grow up with, but for me at my age, umm... old habits die hard.
My own thought is that it will provide temporary protection before its target "bug" mutates to resist it everywhere, as is happening with the "cillin" antibiotics on our time... we got a few decades out of them, we may get a few years in North America out of truvada. I have yet to read of a resistant strain of HIV being detected here, though.