The number of directorships is certainly a product of individual competence but other issues come into play:

1. The complexity of the context and the corporation: the more complex the organisation, the more time and commitment is required. Therefore, fewer additional commitments are reasonable.

2. The role of the director in the corporation and the number of sub-committee commitments required will also affect the ability to take on additional roles. Where the corporation requires limited involvement, then more directorships are possible. The more a corporation requires a director to take on pseudo-executive commitment, then the fewer other commitments are possible.

3. The individual's commitments outside the corporate area also have a major influence on the time available. Where individuals also take on NFP, voluntary, charitable and other commercial activities also limits their productive availability to any particular corporation.

4. The propensity for spontaneous calls on a director's time: if the corporation is in a highly volatile space (calamities, cultural dynamics, union volatility, political volatility, sensitivity to economic dynamics, environmental sensitivity, etc) the more there is likely to be unplanned calls on director time. In that sort of context, it's hard to commit to too many directorship (or other commitments) because of the unpredictability of the context and the inability to "give time and attention" when called upon.

5. Finally, the individual's propensity to accept personal risk: in the current climte of increasing director accountability and shareholder activism, fewer directors are prepared to take on too many commitments (board or otherwise) which enables them to stand accused of negligence through lack of focus.