There are a number of reasons why French press coffee makers can break. The most common reason is that the plunger isn't tightened properly, causing the glass carafe to shatter when pressure is applied. Other potential causes of breakage include using a coarse grind of coffee, overfilling the carafe, or using boiling water instead of hot water. French press coffee makers are also more fragile than other types of coffee makers, so they should be handled with care. If you follow the proper instructions and take care of your French press coffee maker, it should last for many years.