When Philadelphia law firm Saul Ewing combined with Chicago’s century-old Arnstein & Lehr to create a 375-strong legal powerhouse, there were endless numbers, cases and logistics to worry about, but the biggest concern for Jeffrey B. Shapiro was something many disregarded — clashing personalities.

“The numbers don’t matter if the people don’t get along,” said Shapiro, managing partner at Saul, Ewing, Arnstein & Lehr’s Miami office,