What does it mean to "believe" in someone?

"It will not save me to know that Christ is a Saviour; but it will save me to trust him to be my Saviour.  I shall not be delivered from the wrath to come, by believing that his atonement is sufficient; but I shall be saved by making that atonement my trust, my refuge, and my all.  The pith, the essence of faith lies in this a casting oneself on the promise.  It is not the life-buoy on board the ship that saves the man when he is drowning, nor is it his belief that it is an excellent and successful invention.  No!  he must have it around his loins, or his hand upon it, or else he will sink."  Charles Spurgeon
I have daily inspirational words that I read on my phone written by Charles Spurgeon and what is written above was the one for today.  I have been thinking something along this line for a long time now, but never found the right words to explain it until today.  I had to read the words over and over again to grasp what they were saying...pretty heavy stuff.  I thought about a particular verse today that we all know very well:

"For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life.  For God did not send his Son into the world to condemn the world, but to save the world through him.  Whoever believes in him is not condemned, but whoever does not believe stands condemned already because he has not believed in the name of God's one and only Son."  John 3:16-18

If you think about someone you "believe" in, what do you notice about your relationship with that person?  What does it mean to "believe" in someone?  What does that look like in every day life?