Imagine you are floating in a huge ocean current going 95 miles an hour. We'll call this current the conceptual momentum for Gravity. Now imagine that you decide to swim against the current. The fastest swimmer in the world is able to swim 5 miles per hour. Realistically (without tools) you will never be able to swim against the current. (sorry, while I have theories, I have never learned to fly although I've learned some interesting tricks about falling)
However... Even if you can't swim against the current for now, you have other options. You can splash. With some practice you might be able to splash a couple cups of water by adjusting their momentum by 30 miles per hour. Sure, you might not be able to cancel gravity for those cups of water, but you can effect their momentum. I would liken this to my knife throwing practice. I practiced Telekinesis by throwing knives at a target and trying to “bend them” away from their original direction (usually toward the target goal).
If you ask anyone who knows me, I can't throw a Kleenix into a trashcan 5 feet away until I start using telekinesis. However once I start using TK, people have watched cool things like an object without spin lean left around a pole, lean right back on track and then suddenly drop at the end as it would have missed otherwise.
Now, even though I am claiming that there are reasonable limits, I have mistakenly tossed a pot across a room without touching it during a temper-tantrum. Also, in moments of desperation I have avoided falling in ways that I can't align with the laws of physics as well. I liken this to the stories of grandmothers moving cars off of kids during emergencies. Emotional charge and desperate need seem to make it easier and more effective to “break the rules;” however, it's hard enough to study magic in calm and controlled conditions... it's downright impossible to try to study it in uncontrolled conditions of desperate need.