Its Time.
At some point we are all forced to turn down a road in our lives, deliberate or default, that is called destiny. The landmarks (achievements, events, opportunities and the like) are things that to an extent we can control and to another extent we are at the grace and mercy of the One who made us.
Its not inaccurate to say that we could all have possibly been on the road called destiny for longer than we have known but at some point or another we will eventually see and recognize its sign post: the point in our lives where the way before us narrows and our traveling companions begin to take a significant role. 
Like a transition from primary to high school, our lives transition pace. We move from taught to teacher, from  student to young professional, from single to married... its time for the cog of purpose to meet with the cog our heart lives in. For some they cannot define what this purpose is or where its from or may even live oblivious to it and therefor, aimlessly. For the ones who have encountered and know their maker, by unmerited grace they can know Him and although they may not know the exact mapped out rout of their lives, they can know the one who designed them and this world. The rest is a glorious mystery, and no... its not important so don't ask. Just take a step. Then take another step. And another and soon you'll be walking out your destiny.