Am I aiming too high?

I've heard it said many times that in order to be successful at anything in life it is often necessary to take risks. Well, I can't really say that I'm a risk taker and I haven't really been very successful at anything in life. However, I don't believe it's all about taking risks. I believe the reason for my lack of success is due to the fact that I have been somewhat complacent all my life; aiming for superiority but settling for mediocrity. I'm tired of mediocrity, tired of being average and tired of falling short. It's time for me to reach for the sky and follow through but how do I know if I have what it takes? Am I aiming too high?

A couple nights ago I dreamt that I was able to run a mile in less than 4 minutes. So last night with the dream still fresh in my head I decided to go for a run. I started out too fast because I got a pain in the side of my stomach, which forced me to have to slow down. It wasn't until about 2.5 miles later that I was able to increase my pace a bit. I ran a total of about 4.75 miles in about 39 minutes. Not too bad for a beginner I suppose; An 8 minute mile is probably the best I can do right now but I wonder what it will take and how long before I get to a 7 and then a 6. I won't even think about 5 right now but I don't have much time and would really like to get there some day. Am I aiming too high?

A couple months ago I started swimming at a Hotel's pool that I thought was 24 meters wide because that's the information I got from their website. I swim the width of the pool rather than the length. I was making good progress in my workouts but when I looked at some Ironman race results and saw the swim pace of some of the world's best triathletes, I realized that my progress was too good to be true. Today, I decided to get an accurate measurement of the pool and it turned out that the pool's width is only 13 meters. Now I have to go back an fix all my log entries where 1500 meters will now become 800 meters. I can do about 800 meters in about 21 minutes. Not bad for a beginner I suppose and more believable but some day I'd like to be able to swim twice as fast. Am I aiming too high?