Comprehensive and Detailed Explanation From Exact Extract:

Asset allocation is the most critical decision for portfolio success, followed by sector weighting and then security selection. The feedback from the document states:

"The single most important decision, one that accounts for most of the success or failure of a portfolio, is the asset allocation decision, which is the selection of the classes of securities to be held and in what proportion to hold them. The next most important decision is the selection of the specific industries from which stocks will be selected: the portfolio’s sector weighting. The final decision is the security selection: the choice of which individual companies within the industry or sector to invest in."