If we allow anxiety about the past or fear about the future to command our attention, we often mess up the present. Ride in THIS moment. It is what is happening NOW that counts!
If a horse is anxious, he's only anxious about what is happening in this moment. If you notice horses grazing, something might spook one and they run, but seconds later they are head down, back to their restful grazing state. They aren't dwelling on what spooked them, nor are they worrying about what might happen next. They are totally present with their mouthful of grass.
We can learn so much from our horses. If we stay totally present in this moment, with whatever is happening right now, accepting it as it is, all our anxieties drain away. Anxiety only exits because we dwell on it and lose our attention on 'now'.