When setting anchors, we are looking for something really stable to anchor to. Some great examples are live trees over 6" in diameter, boulders that weigh several tons, solid manmade features, etc. This type of a bomb proof anchor is essential for One point anchors systems.
What can you do if all you have are marginal anchors? This is where multipoint systems need to be used, preferably with some type of backup tagline. A key safety practice when using multipoint systems is small deep angles to avoid a vector pull. Here is a short article on Two point anchor systems.