I hear ya! Some of us are just clumsy though.....! I am very careful with my expensive items - but clumsiness wins out far too much. The problem with being clumsy is that no matter what you do to try not to be, you're still clumsy (and sometimes trying too hard makes you clumsier!).
The easiest way to describe it to most people is that it's like when someone's sleeping and you're trying to be extra quiet, but the harder you try the more noise you make....
Two people that don't know each other have each hailed me "the clumsiest man in the world".... So, although I don't want to use a case and protector, it makes sense if I want to sell the device a year later....
Oh, I'm clumsy. Very.
But in the back of my head more is "I can't afford to break this device." so I use two hands, place the phone in specific spots, etc, etc.
To be honest though, I dropped my iPhone 5 several times and my iPhone 6+ I dropped ONCE. Just once cracked the screen. I have dropped my 6s+ a few times but never more than a few inches. There have been some higher drops but those all happened on carpet.
Both my 5 and my 6 though, through forcing myself to handle them in certain ways, over time have put muscle memory into me so that subconciously I am protecting the device when it's in my hands.
Which is not to say I'm not still clumsy.
PS., I work with a woman who can trip herself on flat and even ground. She's broken more of my stuff than I care to count by her lack of attention. Hence a lot of my protective measures at work to keep my phone the hell away from her!