Student or Learner
Linda: I knew I could count on you.
question : why 'knew' is used instead of 'know'? Any difference?
If it was now you'd say ; I know I can count on you.
Turn this into past tense and you get "I knew I could count on you."
It means that Linda counted on him/her in the past, and now, it turned out that she was right having done so.