Wow, I must be the only person on here who has never had a real riding lesson.
Before I got my first horse I was just a horse-crazy teenager who had only ridden rental horses with no real experience actually controlling a horse (the rental horses just followed the horse in front of them).
The first year with my first horse was a bit tough mentally, but I made it through and I have been a horse owner for the last 18 years or so. Besides not having lessons, my first horse was an Arabian (who was very sweet and lazy actually) and I rode him about 1/2 the time by myself out on the trails. So yeah, we had a few challenges in that first year. Mainly my stupidity from not having any experience, the horse was a saint.
Lessons are great if you can do that. I'm sure I would have gotten to be a much better rider much faster with lessons. But I did just fine without them and 18 years later I actually have a great seat, soft hands and am still riding the trails either alone or with friends.
Getting the right first horse is of utmost importance. I agree with everyone on that. Even after owning horses for so long, I still try to be very, very careful in choosing the right horse to purchase. The right horse is a dream come true. The wrong horse is a dangerous nightmare.