I am the polar opposite of this and I am going rather well with it. Which means: I am happy with what I am doing, I am happy with the money it produces, I am happy with the way customers interact with me.

And quite frankly it would very likely bore me to focus one one thing only. I am not on this planet to get bored with my life or hunt for some mythical sunlit uplands by betting all my time and energy onto one thing, unable to keep a healthy distance riding it into a ditch because I want it to suceed too much. I want the things I create to be objectively good. For this I have to be able to keep a distance to them. Making them the sole center of my life would prevent me from that.

Apart from that I am easily the most productive person in my social environment, parts of which are of the "only focusing on one thing"-crowd. However I don't think my approach works for everyone. There are types who need these context switches and there are types who need that focus.