I recently bought a case of my favorite guitar strings for my PRS, my main gigging guitar, and put a fresh set on before a show.
Halfway into the third set I broke my "B" string, which is highly unusual. I have used this same brand and gauge of strings on this particular guitar for many years, so I am normally pretty confident that I can get at least a couple of gigs out of a set before changing them.
Thinking it was a fluke, the following week I put on another new set of strings before the gig. Then it happened again. The new "B" string popped about halfway through the show.
My first thought was that I got a bad batch of strings. It happens occasionally, but it's rare.
Sure enough, the next week came around - another new set of strings - another "B" string breaking in the middle of the gig. I knew I had a problem.
Usually guitar strings break because they are too old. They reach the end of their life expectancy and just give out. Every guitar is different, but we all get a feel after playing one for a while, how long a set of strings will last, and know when it's time to change them.
But if you're breaking strings more often than normal, and it's the same string that's consistently breaking, the first thing to do is pay attention to "where" on the guitar that string is consistently breaking.
Quite often, there are three areas the string will break - the "nut of the guitar, the "strumming" zone, or the "bridge".
Once you determine the location of the string break, you can usually diagnose the problem, as well as the cure.
The "Nut" - A guitar string may be "binding" at the nut of the guitar and not allowing the string to flex properly in reaction to the normal fluctuations in string tension caused in the normal course of playing. This can cause undue tension on the string at the point of contact and result in a break. Adjustments can be made to the nut to allow the string to move more freely across the nut and alleviate the problem, or the nut can be replaced altogether.
The "Strumming Zone" - If the string is breaking at the area of the guitar where you are strumming - across the sound hole on an acoustic, or the pickups on an electric guitar - then the problem may be caused by a change in pick thickness, or an increase in strumming hand "attack" on the strings. Often, a change to a lighter gauge pick, or easing the attack on the strings when playing will solve this issue.
The "Bridge" - If the string is consistently breaking at the bridge of the guitar, then you may have developed a "burr" on the bridge. A burr causes a "catch" on the normally smooth part of the bridge saddle, resulting in a break, and is not uncommon. The problem is solved by re-smoothing the bridge saddle to remove the burr.
If you are experiencing an abnormal amount of string breakage, and it's occurring on one particular string, then try to pay attention to the location of the break.
If the break is consistently occurring at the nut or the bridge of the guitar, then take it in to your local music store and have a guitar tech take a look at it. There is usually an easy, and fairly inexpensive, fix that can be done.
You'll be glad you did, not only for the sake of making your strings last longer, but also in the reduction of the frustration of popping a string at the most inopportune moment!