While there are a number of recommended contents of the portfolio strategic plan, a guiding principle is to:

Documenting assumptions and constraints is a recommended content element within the strategic plan, but it is a supporting artifact rather than the overarching guiding principle.

Recognizing stakeholder risk tolerances is an input consideration for portfolio risk management, not the guiding principle that establishes the strategic plan's fundamental purpose.

Progressive elaboration describes how a portfolio evolves iteratively over time, which is a characteristic of portfolio management in general, not the guiding principle specific to the strategic plan.

Defining the portfolio vision and objectives to align with organizational strategy is the primary guiding principle because all portfolio components, investments, and decisions must trace back to and directly support the organization's strategic goals. Without this alignment, the portfolio lacks direction and justification. The PMI Standard for Portfolio Management identifies strategic alignment as the core purpose driving all portfolio planning activities.