By the way, did somebody take you for an ISTJ (as I was taken for an INTJ before)? Just wondering.
The functions can be perceived as similar since they, at least for me, compliment each other. I use intuitive reasoning to overcome my Si´s major problem: missing, if nonexistent, information. I always start from what I know and what I see (the facts), and then start putting them in perspective (juggling with different possibilities and unseen patterns) to figure out how a situation will develop, or in which context it is situated, in order to get a solution, or a plan, which can be helpful also in the long-term.
There must also be intuitives who can follow this same process the other way round.