It has been one hundred percent effective. If I miss a day, I know (and so does everyone else). We (psychiatrist and I) tried to see if I had gotten past the point of needing it by tapering off. Didn't work, so I'm back at ten, probably for life. That's fine, there's way worse medications to be dependent on!
A small point, but the "discontinuation effects" for these meds can be severe, and they can make people think they still need to take the meds. This keeps people taking meds for very long amounts of time.
Some people are okay with the side effects, and they've made an informed choice about the risks of taking these meds long term.
The Guardian newspaper has been running a couple of stories about long term use. I think they're a little bit alarmist, but the personal experiences are useful.
https://www.theguardian.com/society/2017/may/06/long-term-us...
https://www.theguardian.com/lifeandstyle/2017/apr/03/is-brit...
https://www.theguardian.com/society/2017/may/06/dont-know-wh...
The experience of others doesn't mean a darned thing. Each person's biochemistry is highly individual which is why the success rate of treating various mental disorders using medication is so low.
I, for example, get rapid tolerance to just about everything, so even the few SSRIs that worked didn't help for long.