3 of 4 added 13 characters in body

All the cowards complain

A bird, a plane?
I am more like the rain
"Stupid", "insane",
all the cowards complain
Near the end of the run,
I slowed my pace
And thence ended the fun,
and my heart's race

What am I?

No offense for using the word "coward", just a figure of speech.