My husband, a geologist, travels off-road when he's doing field work. The best rock outcrops are off the beaten path, sometimes miles from a paved road. Before our daughter was born, I'd sometimes travel with him. When he used to take me along, I usually had a white-knuckled grip on the door handle. The more the Jeep tossed us around, the better. He loved it. Me, not so much.
Like the driver, a main character should be living the story instead of watching the events take place. It's that old 'show, don't tell' conundrum: let the MC loose in the scene instead of relegating him or her to the sidelines.
Take the following paragraph for example:
Ellie saw the horse running toward her. She was afraid, too afraid to move. As it got closer, she noticed the whites of its eyes as the horse grew more panicked. It kicked up its back legs, one hoof knocking the top rail from the fence. She knew she should run. It was too dangerous to stay put.
By using words like Ellie 'saw' and 'she noticed', our MC is observing instead of participating. Also, by telling us she is afraid, we don't really know anything more about Ellie's frame of mind other than what's on the surface. Show us she's frightened by how she looks (eyes wide, fists clenched, etc.), what she says or thinks ("I'm outta here!), and what she feels ('My heart pounds like the hoofbeats I feel shaking the ground beneath me'.). Here's an example of Ellie taking charge:
The horse kicked up dust as it barreled toward Ellie. Ellie's stomach lurched. There was no where to run to; the barn was too far. She'd never make it.
"Stop, you stupid horse!" she yelled at the top of her lungs. She threw the bridle to the ground in front of her in disgust. It uncoiled, twisting like a blue snake.
Sliding to a halt, the horse reared up when it saw the bridle twisting in the dirt. Its flailing hooves blew the hair away from Ellie's face. Tears stung her eyes.
"I can't believe I ever thought we'd be friends, that I could ride you," she said through gritted teeth.
In that section, we get a sense of what Ellie's feeling by her physical and emotional reaction to the horse. This is accomplished by using dialogue, action, and avoiding the passive tense.
If your MC seems to be taking a passive approach to what's happening, stop the car. Get out of the driver's seat and let him or her take over the wheel. Then hang on and see where your MC takes you.