When a trail has no flow, and is abruptly popping users into one feature and then the next, is usually when the differing user groups experience conflict. And conflict usually means treadwear. Treadwear is bad. Yep folks, the sustaining factor in our human lives is very detrimental to trails. When designing new trails it's important to keep the water off with the proper design.
Good planning helps with sustainable and easily maintained trails down the road.
A rule of thumb is that your planning should take as long as you're building. Focused water does the most damage, therefore, keep in mind how to plan for the water to be 'broad' and unfocused. This involves things like waterbars to direct the flow of the water. Other features, like full bench construction including blending the back-cut into the backslope, will allow water to roll off the trail properly. On existing trails that have chronic wetness problems, look up the hill or trail.