To "dwell" on something has several meanings. For example, a home is a dwelling. People live in a home, which is to say, they "dwell" there. In this sense, it means to stay in one place. The other meaning of "dwell" is to think about something longer than is practical. A person might worry about money too much, or worry about some past experience too much. That is what it means "to dwell on" something. By the way, the full sentence you cited, is a very poorly written sentence. The author is trying to force to many distinctly different observations into a single construction. It would be better communicated this way: "But you aren’t going to are you? With each step comes the decision to take another. You’re on your way now, but this is no time to dwell on how far you have come." I wonder where this was taken from?

It means, you can't stop, you have to keep going, you have to keep moving forward everyday to achieve what you want. when someone says "don't dwell on something" it means don't waste time on something. The author is trying to tell you that instead of thinking "wow, I done so much and I've accomplished so many things", you should be thinking "what's next?". There are a lot of meanings in that video but I tried to simplify your point in question as much as possible. by the way, Zakaria took this from a youtube motivational video (which is actually an advertisement for Nike). I know it cause I love it! I hear it everyday as my wake-up alarm. here's the video: http://www.youtube.com/watch?v=so0qslHYJpw

I don't have the full context, so I can't be 100% sure, but it seems to be emphasizing that this is not the right time to stop and think about (dwell on) all the progress you have made so far; right now the most important thing is continuing your journey. Hope that helps?

You should mention the source as a link, it would help people better understand the context. Mr. Bruce did a good job of explaining without knowing the true context of that statement. Providing sources helps us to help you better :) Good luck and have fun learning!