Here's the core issue tho.
My character is in a game of power fantasy. He is expected, in the narrative, to do fantastic things. The bounds of our mundane reality are not his reality. I do not find it believable within the genre of power fantasy that he has such limitations is Earth physics. With enough skill, he can leap 30 feet regularly, move faster than Usain Bolt, turn on a dime, while wearing armor made out of metals heavier than any found on earth.
And all this is believable, because he's NOT on Earth. He doesn't obey the laws of physics because he's not in a world of physics. He's in a world of heroes, of legends, of demigods, of the fantastic. He is in a world where one who grasps power can take it and -become- power.
He can't grab a waterfall? Why the hell can't he try? He's not Dwayne Snibblin, computer programmer. He's GORGANASH THE CONQUERER, and with his axe has brought nations to his command.
I mean really... when you watch the LoTR movies, do you cry '








!' when Legolas does that awesome stuff to take down an oliphant? No. Why? Because his world is not the same as ours. What he does is plausible for him to do. He's just as martial as anyone... but he transcends the laws of -our- world by dint of simply not being in it.
When you say something is impossible, you need a better reason than 'It's not realistic' because of the nature of the world you're playing in. In the D&D presented in the books, it IS possible, and it IS plausible, and to claim otherwise breaks versimilitude while Page 42 exists.