Due diligence focuses on the result and its construction: the Sharpe ratio, the drawdown, how the universe was defined, and how risk is controlled. These questions interrogate the configuration the manager chose. They rarely interrogate the configurations the manager did not choose, which is where fragility lives.
Standard robustness checks, where they exist, are usually performed and reported by the manager on the manager’s own terms. The strategy is shown to survive a handful of sensible perturbations. It does not, however, tell the allocator how the strategy behaves across a range of reasonable alternatives another team would have made, or which single component the whole result rests on.
