What makes juggling interesting is that you have three balls but only two hands. So one ball is "out of control" all the time. Technical leaders also keep three balls in motion: What the customer wants, what engineering can deliver, and what will make money for the company.
There is a relationship between these three balls that makes technical leadership interesting. If engineering overbuilds, the customer is thrilled but the business isn't as profitable. If engineering under-builds, the customer will pay less for the product, or not buy it at all. The business puts pressure on engineering both to deliver more and deliver efficiently. The customers and the market put pressure on the business to give them every feature they want at the lowest price.
Good technical leaders listen to all three constituents and throw ideas for how to satisfy everyone. They act as a translator between what the customer wants and what engineering can deliver, with an eye on the business impact.
All three balls are important. As with juggling, if one ball falls it stops being interesting. As a practical leader, you need to keep an eye on all three areas, in a balance that keeps the customers happy, engineering excited about the product, and the business profitable. And, when you drop a ball, pick it up fast and get back to juggling.