Where does divine providence end and free will begin?

Todays Question:  How do we reconcile the concept of free choice with Divine Providence? We have free will, yet Hashem decides all outcomes and designs what is best for each of us. If there is such a fine line between the two, how do we find it and live in that space of a peaceful co-existence? How do we know when we have done enough and when to turn things over to Hashem? To co-create, to build a partnership & a trusting relationship, both sides have to do their part and trust in the process. I have to do my Hishtadlus before I surrender to Hashem for Him to do his part. How can I "feel" into and create a balance between the two?