Got distracted looked over shoulder - oops! Everything falls over. Step back a pace to check the scene - oops everything falls over. Etc etc
Stability of the tripod? Get a decent tripod and set it up properly! My tripods frequently have to help balance / help support me let alone a little 1 series camera and long lens.
Not having a go at you but when I was learning I used to do this with the crappy Manfrotto I had at the time and it is a recipe for a damaged Credit Card

......the strap's around the guy's neck....everything's not going to 'fall over'.
You're really reaching on this one. 


















