Jack Dorsey is Squarely in Control

With his second startup, Square, Jack Dorsey appears to have learned an important lesson from his Twitter experience: It's vital to retain effective voting control.

Mr. Dorsey has 24.4% of Square’s voting shares, the company disclosed in its initial public offering securities filing on Wednesday. That doesn’t sound like a lot, but it's enough. And it’s a big contrast to the situation at Twitter, where he owns only 3.6% while fellow co-founder Ev Williams owns just 7.8%.

That makes Twitter vulnerable to an activist investor or a rival businessman who think they could run Twitter better. The lack of a single controlling shareholder may have also contributed to Mr. Dorsey's ouster as Twitter CEO in 2008 and the continued instability in its upper ranks.