The number one killer of transmissions is excessive heat.
Excessive heat causes the transmission fluid to oxidize and break down, which robs the transmission of it's vital lubrication and also creates severe internal wear.
Although heat is the number one killer of transmissions, other things also increase the excessive heat, which accelerate the death of a transmission.
Having low or contaminated transmission fluid, doing lots of heavy towing and hauling, neglecting maintenance and aggressive driving habits all factor into and cause transmission failures.
Transmission fluid acts both as a lubricant and coolant for your transmission.
And having leaks or old, burnt fluid in the transmission also lead directly to increased friction as well as catastrophic overheating.
It's important to keep an eye on your transmission fluid and never allow it to get too low.
If the transmission fluid is low, you should add some more of the correct transmission fluid and change or have your transmission fluid and transmission fluid filter changed every 20,000 to 30,000 miles to extend the life of your transmission.
And exceeding your vehicle's factory towing limits or even placing any extreme strain on your drivetrain causes the torque converter to slip and generate intense heat, which kills transmissions.
If you don't have a transmission cooler and do any towing, it's recommended that you add a transmission cooler to help your transmission and transmission fluid stay cool.
As for not changing the transmission fluid, failing to change the transmission fluid and failing to replace any clogged transmission filters, allows the transmission to operate with degraded heat trapping fluid, which also kills transmissions.
And even slamming on your brakes, rapid acceleration and shifting gears while the vehicle is also still moving shock the system and spike the transmission fluid temperatures.