What is the burden of proving a breach of contract?

Appellants next contend that plaintiff did not sustain his burden of proving damages resulting from the alleged breach of contract. This contention is without merit. In Stark v. Shaw, 155 Cal.App.2d 171, 317 P.2d 182, in an action for damages for failure to perform a roofing contract it was there contended that plaintiff failed to establish with certainty that the roofing company would have made any profit at all had the agreement been performed and that the evidence was insufficient to support a finding that the roofing company was damaged in any reasonably ascertainable amount by [173 Cal.App.2d 232] reason of the defendant's breach of the contract. The court, in discussing these contentions, said (155 Cal.App.2d at pages 180, 181, 317 P.2d at page 187):