Analysts' consensus forecast for Tesla's earnings per share in 2016 finally slipped into the red this week. A few cuts in the wake of Wednesday's second-quarter results took the estimate from a profit of about 23 cents to a loss of about 65 cents, according to forecasts compiled by Bloomberg. Go back 18 months, and the consensus was $5.49.

If history is any guide, the cuts haven't gone far enough yet.

Despite this history of markdowns, forecasts have still tended to be too generous: Tesla has missed estimates in five of the past six annual earnings reports:

As you can see, those Excel models were especially malfunctioning over the past couple of years. Where analysts were really caught out was the rapid acceleration in Tesla's spending to boost production of the Model S and launch new ventures such as the Model X and the Gigafactory battery facility.