Not quite 100%.

> The early failure rate of vasectomy (presence of motile sperm in the ejaculate at 3–6 months post-vasectomy) is in the range of 0.3–9% and the late failure rate is in the range of 0.04–0.08%.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5110415/

8 out of 10,000 men is still a very low failure rate, although keep in mind that typically failure rates for contraceptives/sterilization are per annum.

So if you get a vasectomy with a 0.08% failure rate and then have sex for 30 years ... 0.08% * 30 = 2.4%.

To be fair, that's still a better 30-year failure rate than most contraceptives:

Typical hormonal IUD annual failure rate = .1% [1].

.1% * 30 years = 3%.

Considering that one would have to get the hormonal IUD replaced (painful!!) every 3-8 years [1], while vasectomies only require check-ups two times after the procedure (not painful) after 1-2 months, and at one's discretion afterwards, that's a way better value proposition.

Generally the control for this is 3 months after the procedure you get a fertility test and a secondary procedure if needed.

Thanks for sharing your positive experience - it's great to hear that the procedure was painless and quick, and has given you and your partner a reliable form of contraception. More important, having a close person in your life whom you can trust is truly a life jackpot! In the current "epidemic of loneliness," it's more important than ever to have strong personal connections.

That's all well and good but there are a lot of situations where women go for birth control where that isn't much of an option.

I certainly didn’t say anything to preclude that. In fact unless the woman is certain of the man, she should control her own contraception. The consequence of a mistake falls disproportionately on her and, well, men are pretty much all assholes, even the well intentioned ones. My message, though, was for men - not for women. Vasectomies are a man’s choice, and the only one we can make that fully insulates the woman in our life from the consequences of sex. Any other measure a man can take is pretty poor in it’s effectiveness.

A few of my friends have looked into this and decided against because it is actually not as reversible as they initially thought.

What did your doctor tell you about reversibility?

Yes. Upshot was usually reversible but with reduced fertility, but even when not IVF works because machinery still works and you can clear some sperm even if not successful. So, yes, I waited until I was “done,” and that’s probably the right way to treat it. But even so you could still have kids even in the worst case with some science assist.