In my experience with sharpening, I found that I wasn't getting to the tip on a lot of knives. Once I started caring about the tip and paying attention to it, I found that I was not using the proper angle at the very, very tip of the blade, causing the last 1/8" - 1/16" to not touch the stone. In these cases, it was because I was not raising the handle high enough to maintain the bevel angle.
Also, importantly, I found that it helped me a lot to push the point of the blade more forward than sideways. This is a natural motion as you go through the belly, to change the angle of approach to be more and more forward. Exaggerating this a little at the tip helped *me* to get much better results.
I discovered the problem and the solutions by first seeing that my tips weren't all that sharp, then using sharpie to observe where I was grinding. When I found I wasn't removing the sharpie at the *very* last bit of the tip, I changed the edge angle, and the approach angle until I got there. I also found it very helpful to look at the tip under a 10x loupe. Grinding, observing, and repeating allowed me to see the tip get re-shaped as I went. It's pretty cool to watch the rounded profile change to pointy. You can look harder, or use higher magnification to then refine "pointy" into extremely pointy.
To echo what Jason said, it's deceptively simple to get it right. Just grind up to the tip, at the correct angle, and stop. Figuring out the correct angle and when to stop was the challenge for me, and sharpie plus loupe made that pretty easy actually.