When does a company's duty shift from shareholders toward creditors, and why does that 'zone of insolvency' matter for directors?

As a company approaches insolvency, the economic stakeholders change: shareholders are increasingly out-of-the-money while creditors bear the downside, so directors' duties shift to take creditors' interests into account (in the UK clarified by BTI v Sequana; in Germany expressed through filing duties and §15b payment restrictions once Insolvenzreife arrives). The 'zone of insolvency' matters because decisions that benefit shareholders by gambling with creditors' money — continuing to trade, paying dividends, preferring some creditors — can later be challenged and expose directors personally. Practically, directors should document that they are monitoring solvency, taking advice, considering creditor interests, and not worsening the creditors' position. It's the legal backdrop to why boards engage restructuring advisers early rather than trading on in hope.