Keep your heart with all vigilance, for from it flow the springs of life.
Proverbs 4:23
Long Before Hollywood Script Writers with DISEASED IMAGINATIONS to pass from their heads to a storyboard to a Script to your box office or TV-- there was Bradwardine....just saying...
"Medieval monks had a terrible time concentrating.
And
concentration was their lifelong work!
They
complained about being overloaded with information, and 
about how, even
once you finally settled on something to read, it was easy to get bored
and turn to something else. They were frustrated by their desire to
stare out of the window, or to constantly check on the time (in their
case, with the Sun as their clock), or to think about food or sex when
they were supposed to be thinking about God. They even worried about
getting distracted in their dreams.
Say that you wanted to learn the sequence of the zodiac.
Thomas
Bradwardine (a 14th-century university master, theologian and advisor to
Edward III of England) suggests that you imagine
a gleaming white ram
with golden horns,
kicking a bright red bull in the testicles.
While the
bull bleeds profusely,
imagine that there’s a woman in front of it,
giving birth to twins,
in a gory labor that seems to split her up to
her chest.
As her twins burst forth, they’re playing with an awful red
crab,
which is pinching them and making them cry.
And so on."
PocketWorthy