The guitarist in our band gets through strings amazingly quickly. I play guitar too, but in the band I'm the bass player. I play electric with my fingers and nails, I've never used a pick - just not for me. In 30 years, I've probably broken less than 10 strings, and I never swap them just because they've been on a long time. I wipe down, and that's pretty well it. I'm not a loud player, but I do bend quite a bit - using 9s on some guitars and 10s on another.

Today, our guitarist snapped the low E strong - and after we'd all thrown things at him he became really defensive, insisting most players have this trouble. He said that as we'd been playing 60s rock 'n' roll, this was why the string snapped. It seemed to have snapped about where he'd hit it with the plectrum. Maybe I've just been isolated from this, but I have never snapped a low E string in my entire life. Is it me?
He's got a burr on the string saddle., or he's picking like a butcher. Blaming it on playing 60s rock and roll is laughable. Does your drummer break a bunch of heads playing polka music, too?
I've been playing for 12 years and probably broken 3 strings. I don't think this is a common problem for most people. I do have a friend in a punk band that breaks a string almost every time he plays though. Just how some people play I guess.
If his pick is too much in an angle, it does exert more slicing force on the string.

If you could somehow get a video of him playing

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When I started playing electric, I used to break strings frequently on both of the guitars I owned at the time.

I took them to a tech to ask him about it, and he said it was probably a burr. In the intervening decade, I have averaged less than 1 string per guitar per year. (I have lots of guitars, and I rarely break strings.)
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I have very acid hand and I used 4-5 sets of strings per year ( one set didn't last more than 1 month). Maybe it is what is happening to him.
If it is the problem, just make sure he has his hand well hydrated and that he washes his hand often
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Thanks guys - I was beginning to think I was a dinosaur! I've not got a video, but I do notice in many photos, his pick hand is always up high, so maybe he does just play like a hammer? In our band it's Beach Boys - but his other band is a metal one - so maybe the habit transfers across!
Ironically someone who plays blues (or other lowish gain stuff) need to play more aggressive for a good soulful sound (where the headroom is present to be filled with dynamic goodness), where's a metal guitarist hardly needs any force.

There's a volume knob, and with high gain the max attack before hitting the dynamic's highest point is so low..

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Who's Andy Timmons??
When I play I hit my string with the force of my shoulder and my arm, so I hit pretty damn hard.

I don't have a problem with strings breaking too often though, not sure what it could depend on. If you rehearse in a garage and your guitarist leaves the guitar there during the night, it wouldn't suprise me in the strings would take damage from that.