Some trees have structures that are prone to failures. This doesn't make them unhealthy, but it does mean they have the potential to be hazardous. Trees with multiple "tops" and stems, insecure attachments (where two stems, or trunks, come together), plus opposing forces from limbs, leaves, seeds, and possibly ice/snow - are more at risk. In conjunction with thoughtful pruning to take weight out of said stems - cables, bolts, and braces can be installed to help. Cables are proven to be able to catch very large material before it falls to the ground or on a home, street, etc. Bolts and braces can help support a tree before it fails. There are different types of all of these support systems, and each has their time and place. If we see a tree that could benefit from supplemental support, we will let you know during our visit!