From this passage, tell me what was Osborne Computer Corporation's mistake.

The Osborne effect is a social phenomenon of customers canceling or deferring orders for the current, soon-to-be-obsolete product as an unexpected drawback of a company's announcing a future product prematurely. It is an example of cannibalization.
The term alludes to the Osborne Computer Corporation, whose second product did not become available until more than a year after it was announced. The company's subsequent bankruptcy was widely blamed on reduced sales after the announcement.
The Osborne Effect states that prematurely discussing future, unavailable products damages sales of existing products. The name comes from the planned replacement of the Osborne 1, an early personal computer first sold by the Osborne Computer Corporation in 1981. In 1983, founder Adam Osborne pre-announced several next-generation computer models (the Osborne Executive and Osborne Vixen), which were only prototypes, highlighting the fact that they would outperform the existing model as the prototypes dramatically cut down assembly time. A widely held belief was that sales of the Osborne 1 fell sharply as customers anticipated those more advanced systems, leading to a sales decline from which Osborne Computer was unable to recover. This belief appeared in the media almost immediately after the company's September 1983 bankruptcy:

To give the jazzy $2,495 Osborne Executive a running start, Adam began orchestrating publicity early in 1983. We, along with many other magazines, were shown the machine in locked hotel rooms. We were required not to have anything in print about it until the planned release date in mid-April. As far as we know, nothing did appear in print, but dealers heard about the plans and cancelled orders for the Osborne 1 in droves. In early April, Osborne told dealers he would be showing them the machine on a one-week tour the week of 17 April, and emphasized that the new machine was not a competitor for the Osborne 1. But dealers didn't react the way Osborne expected; said Osborne, "All of them just cancelled their orders for the Osborne 1."

Osborne reacted by drastically cutting prices on the Osborne 1 in an effort to stimulate cash flow. But nothing seemed to work, and for several months sales were practically non-existent.

Pre-announcement is done for several reasons: to reassure current customers that there is improvement or lower cost coming, to increase the interest of the media and investors in the company's future prospects, and to intimidate or confuse competitors. When done correctly, the sales or cash flow impact to the company is minimal, with the revenue drop for the current product being offset by orders or completed sales of the new product as it becomes available. However, when the Osborne effect occurs, the quantity of unsold goods increases and the company must react by discounting and/or lowering production of the current product, both of which depress cash flow.

It's widely believed that Osborne Computer Corporation's bankruptcy was caused by the premature announcement of some highly performant successor models to their flagship Osborne 1 personal computer. The announcement was initially restricted, but as the news spread dealers cancelled orders for Osborne 1 in droves. The company drastically reduced the prices of Osborne 1 in reaction. This, however, didn't stop the decline in sales.