Hopefully no one is pulling the leash. The ideal situation is that you and your dog are equally enjoying the walk and neither is pulling and tugging the other in any certain direction.
If your dog tends to be pulling you off into its own direction a large amount of the time you are walking, you can train the dog to stop doing this. What's interesting is that you have actually been training the dog to do this behavior not only by allowing it but by supporting it without realizing it.
There are various reasons that cause a dog to automatically pull on the leash. For example, when a beagle sees a squirrel or other animal scurry quickly across in front of him, he is going to go berzerk. You can count on that. So be ready to hold on strongly if you plan to keep the beagle in tow in a situation like this.
Just holding the dog in tow is not enough, though, since this will reinforce the dog's desire to pull. Think of it as a training opportunity! To use it as a training opportunity, you'll need to know exactly how you're going to train.
Another example that will cause your dog to pull you off course is when your dog wants to sniff out an area, he will automatically go to the area with no thought of you who are on the other end of his leash.
Expert trainers have techniques to keep a dog focused in the direction of your choice. You want to take care not to reward the dog when he goes off your chosen path and expects you to go with him. Since it takes you by surprise, you may inadvertently reward him by following him, impulsively reacting to his sudden behavior.
Now you may take a look at what you are doing that is rewarding this behavior. You say,