Once it starts rolling, it’s not clear how far it will go. In any case, the brush keeps moving.

I like this. Sounds like one can have multiple drips going at once, including some that hve been dripping for a long time.

Eventually the last drip stops and a new one starts.

Is this sentence saying that at some point the multiple ongoing drips might stop (or slow to a crawl), but the person is still learning, because they're already starting new drips?

I'd prefer to avoid misinterpretations of short-attention-span or serial-dabbler.

Also, the characterization of T-shaped here speaks of interests, but the motivations for skill development might actually be necessities, such as in an early startup. The interest can be a side-effect of something needing doing. You start to dig into the solution domain, anchored around a real problem, and it becomes interesting.

If only we could be comb-shaped.