.

rainwater makes the tarred surfaces slick
ça glisse!
you shouldn't make your usual strident gait
especially if you are wearing sandals
you can lose your grip,
and your forestretched foot will slide out further than you like
and your leg tendons get strained
you will probably regain your balance
then think how close you came
to knocking your knee
and muddying your blouse

but this would only happen on a tarred surface
sidewalks usually don't have this problem
but since it's raining
and you have the chance to drive
you wouldn't prefer the sidewalk
unless it's a light storm
and you carry an umbrella