Matter of fact, it's gravity that pulls one so (4,2,5)
I believe the answer is:
down to earth
'matter of' is the definition.
'down-to-earth' can be an answer for 'matter' (thesaurus). I'm not certain of the 'of' bit.
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for down to earth that I've seen before include "Plain-speaking" , "Sensible and practical" , "Without pretension" , "where parachutists come?" , "Plain" .)