How can you use a condom incorrectly?

Question

Serious question, they say condoms are like 85% effective because people don't use them correctly but if used correctly they're more like 98% effective at preventing pregnancy. 
I just don't understand how someone can use a condom incorrectly.. you just put it on the penis and that's that! Am I not thinking outside of the box or what?

Edit
Thank you ladies! That did help, I guess I just wasn't really thinking of the little things!

Answer

I think, not sure, but I think a condom can be put on upside down causing it to back up during sex. Also, you're supposed to pinch the top where there is excess air. We haven't used condoms in probably 5 years but I know there were actually directions on the box.

Answer

Some people forget to pinch the air out of the tip when putting the condom on so there's a place for the sperm to collect
Condoms sometimes rip during sex
Leaving condoms in the wrong conditions, like in the sun or in a wallet or pocket can wear them down
Some people don't know they shouldn't use oil based lubes 
Some sperm accidentally spills out when taking the penis out and gets in contact with the vulva
Person takes condom off and penis touches vulva again without washing first and there's leftover cum. 
It's all just natural human error. It's not like sperm magically seeps through the latex, hopefully this answers your question?

Answer

Some people think they only need to wear a condom for the ejaculate and that they can raw dog it before that. Sometimes it breaks because its not put on correctly. If you put lube on the inside, it can slip off. Keeping a condom in your wallet for too long. Theres a ton of ways that people can fuck up a condom

Answer

I think alot of people forget to pinch the tip to leave air which results in broken condoms

Answer

If you don't pinch the tip, air can get trapped in there. 
Also you need to use the right size so it doesn't break if it's too small or slip off if it's too big for him.

Answer

I have had a few condoms break. We thought we pit them on right but not sure what went wrong

How can you use a condom incorrectly?

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