OP, you need to work on your willpower. 
As for me, I am still rockin' my 2016 iPhone 7 Plus, and will likely keep it until 2020. 5G or bust!
OTOH, I just bought a 10.5" iPad Pro 6 months ago, and will likely buy the next 11" iPad Pro whenever that is. However, I can blame my wife for that, since she wants that iPad Pro for herself, so I have an excuse to upgrade.
As for me, I am still rockin' my 2016 iPhone 7 Plus, and will likely keep it until 2020. 5G or bust!
OTOH, I just bought a 10.5" iPad Pro 6 months ago, and will likely buy the next 11" iPad Pro whenever that is. However, I can blame my wife for that, since she wants that iPad Pro for herself, so I have an excuse to upgrade.