[Linamium]

For any of you cs go pros out there can 1 of you explain to me how cs works,i was one day just chillin like i always do and 4 some reason i thought it would be a great idea to hop on some cs.So i do that i start playing a deathmatch and in the begining everything seems normal.I would aim normally and eliminate people,but then 4 some reason on some occations when i would aim at peoples bodies or heads the bullet wont go there it just completely goes somwhere else i would miss the player for no reason when my aim was perfect 
  
and of course i would die.
Now can someone please explain why this happens?