That's an incredibly vague standard and courts have repeatedly declined to get involved in second guessing management decisions. Aside from outright fraud or negligence executives can claim almost any business related decision is in the interest of shareholders because they have a reasonable expectation that the future benefits outweigh the costs. Judges aren't going to be delving into financial projections and expense reports to override the leaders of a business.

A widget company could sponsor a soccer team or whatever and say the costs are worth it. Or that same company could not do that and say it's not worth it. Two opposite decisions that both would count as acting in the interest of shareholders.

This case was specifically about dividends and long term shareholder value, not quarterly results.