[Grazester]

If a condom doesn't break then it's 100% effective. When a condom breaks you fails in a manner that you will know it failed and then there is PEP.

[huytersd]

I think there’s a chance of getting it if the condom rolls/bunches up as well.

[Grazester]

This usually the result of poor condom use/knowledge, like condom breakage. If the condom is too big this can happen or you become flaccid(it's a thing to also check to make use that this isn't happening during intercourse), and condoms can break when you don't use lubricant or the incorrect lubricant(e.g. petroleum jelly based lubricant).

[FFP999]

There's no such thing as "100% effective".

[Grazester]

Abstinence is as they like to tell you. But really most of the margin for infection for condoms is the result of poor use.

[Gibbon1]

Yes the quoted effectiveness is based on the average in practice. Anecdotally what I've seen is the failure of condoms is usually got drunk and didn't use one. In particular substance abuse is highly correlated with unsafe sex and HIV infection. I'm pretty sure it's also correlated with birth control failure.

[FFP999]

Ok sure, abstinence, but talk about cutting off your nose to spite your face.