ideas summarised for beginners :
ONLY use glasses that match the strength of the activity, so never wear a minus for up close activity
for example, a man is -5 in both eyes
for looking at mountains, the moon, and into the distance, your full strength lens is safe to use at -5
for reading, sewing, etc, read at the point of blur, OR, with a plus lens
for day to day activities, like basic walking, street signs, a weaker prescription can be used, like a -4.
my point is, every activity in life requires a different "prescription"
myopia is caused by prolonged close up work
never use an overprescribed lens, for example using -5 lenses when a -2 lens would easily work for you
I am not saying these ideas are absolutely correct, if you disagree please correct me