Is in the first horse you manage to climb up on, whether you're 11, like I was, or mid-50's, like I am now. The first horse that I ever rode was a belgian cross almost blonde-chestnut-roan gelding named Mike. Four white socks, a big white blaze, a picture of big and solid and square. A bit short-necked, a bit big-headed, and just HUGE when he is your first horse you ever ever ride.
I rented a horse, named Mike. I was so excited, I paid for an hours time, all of my savings from 11 year old allowances. I had found my first barn, filled with horses.
I was vaulted up onto his broad back outside, in an attached paddock, and turned loose with the rest of the rental string. I was over the moon. I was eleven. Mike ran back to the barn.
What?? I was mortified, embarrassed, my crimson face a subject of laughter from the people in the barn. One of the stable hands led me back out to the paddock, and asked again, "Do you know how to ride?"
"Yes" I lied, again.
Off went the guy, and Mike again, ran back to the barn. And again, back out to the paddock, and whoosh, back again.
I finally answered, in a whisper, "No". That was my very first lesson.
Always be honest, or your horse just might point out when you're lying.
And obviously, take riding lessons, if you don't know how to ride.
I went on to successfully "master" Mike, and we won my first ribbon together. Over jumps, even. Mike was a super cool horse. He would do whatever you said. If you said "I can ride", he'd feel your body truthfully trembling "I've never ridden before in my life!" and back to the barn he'd go.
Mike was for people who answered "Yes" truthfully.