SAN FRANCISCO — David Cheriton is one of Silicon Valley's technology success stories. He's started a string of companies, made millions as an early investor in Google Inc. and is said to be worth more than $3 billion.

But none of that spared him on Tuesday from a taxing cross-examination by Latham & Watkins partner Douglas Lumish on the second day of a trial between two companies Cheriton helped launch: Arista Networks Inc. and OptumSoft Inc.

The facts of the case—which center on TACC, a platform used to write software code faster and with fewer errors than human engineers—are complicated.