i always get nervous when people want to battle me, and they use legendary pokemon.
the reason why is because i am relativity a good competitive layer, and i assume the person wanting to battle is also, just like that.
and i assume their legendary pokemon have nice/good IV's and have an EV spread that fits that specific pokemon.
but most of them don't, ( or they do and i get either lucky, or have my mega gyarados with 1 or 2 dragon dances up, and therefore outspeed most things )
my legendary pokemon ( or the few that i have at this moment )
are either too fast or too bulky to take down easily ( or in one shot )
and i always assume that theirs is just like that.