I rode one horse for 13 years, trusted him 100%....then I bought a 7 month old and brought him up myself until I took him to a trainer at 4 for in saddle training. He came along nicely and I started taking lessons with the trainer. Sometimes the trainer would ride him for 20 mins or so before I rode. I was nervous at first, but I'm at the point that I just got on my big girl pants and just said ... we are doing it. He has tested a few times, and with what I have learned from the trainer I'm able to deal with the situations. I take regular lessons still, and have come a long way as a rider. I just said the other day that I'm willing to "go the distance" with him without thinking of the "what if's" and I know that my horse knows it now. I don't think of the what ifs anymore, I just ride and deal with situations as they arise. Determination and courage is needed and once you are in the saddle your horse needs to know you are in charge, you feel it, you know it and they will too. Just do it!