I disagree it is easy to land gear up. It is the most preventable accident there is.
My initial instruction on a retractable gear airplane was done by a crusty X RCAF QFI. He beat into me that on final when you go through 500 AGL or roll wings level on final you check "gear down". He made me verbalize it every time, something I still do (although now softly enough that nobody can hear me).
I religiously did that for over 20 years and saw the 3 green lights every time until one day a few years ago they were not there on short final. It was the classic case of multiple changes in the plan, cockpit distractions and time pressure broke my concentration and I forgot to lower the gear, but that ingrained habit saved me.
It can save you too if you are willing to exercise the personal discipline to make the gear check a habit and beat yourself up if you ever miss the call.