Life has turning points, including a life of experiencing God. As God calls you into relationship and to join him in his work, there are at least two major turning points where you could miss experiencing God working through you: a crisis of faith and the (in)ability to make major adjustments (Henry Blackaby, Realities 5 and 6 of Experiencing God). While Abraham had several turning points in his life, these are best illustrated in his relationship with Ishmael. 
Scripture:   Genesis 16, 21