The hardness properties of a wood finish are formulated around the objectives of use. A hard finish is desirable on projects that get heavy wear such as kitchen cabinets or table tops.
But in other situations, such as an outdoor topcoat, a desired property of the finish is elongation, which allows the topcoat to expand and contract through different extremes of temperature.
A flooring finish is another example where hardness is not the major objective of the formulation. Just like outdoor furniture, wood floors expand and contract through the seasons of the year, responding to heat, air conditioning and changes in humidity. The floor finish needs to elongate or flex as the wood moves.
This can be problematic for floors which are often subject to heavy use, including dogs nails. Pet nails will not scratch a good floor finish all the way through the wood, but the nails will indent or imprint the surface of the floor.
It is impossible to combine equal properties of flexibility and hardness in a floor finish, so you have to accept some limitations at the outset. You can improve the life of your wood floor finish by selecting a denser wood for your floors, hickory, maple or white oak instead of pine for instance.
Or just live with the indentations. This is another instance where dogs rule.
Heavy sunlight will also affect harder finishes applied in sun-saturated areas such as window sills, causing finishes to become brittle and crack.
You can keep costs down and have a better result if you match the properties of the finish to the needs of the project.
One of General Finishes hardest water based topcoats is General Finishes Enduro Conversion Varnish, which requires a catalyst and is recommend for use by professionals. It cures in half the time of most topcoats, allowing the finisher to pack and ship sooner, but the price point would make it overkill for other uses. Other factoids:
It is impossible to combine equal properties of flexibility, hardness and chemical resistance in a finish, so be sure to select the correct product for your finishing project.