Sunlight itself can cause profound visibility problems, and in every case the issue arises when you’re looking toward the sun. Haze can become impenetrable in that direction, where lakes or other large reflective surfaces are the only things visible. Flying toward the sun in extensive rural or wilderness areas, you may have zero ground reference – except behind you.
High ridges with sun low byond them appear all black, and depth perception can be nil, even very close. Backlight reflecting inside the canopy makes this problem even worse. The only way to see useful detail on a hill in this situation is from below its top, down in the shadow.
Regarding traffic, think of this: from the earliest aerial combat, pilots have been taught to attack ‘out of the sun’, a shrewd strategy that makes them impossible to see. Thus, if you are looking away from the sun and see another aircraft clearly, its pilot may never know you are there! Sunward aircraft at your level may be visible enough through the high sun of mid-afternoon, but at day’s end it’s best to assume that you cannot see anyone between you and the sun.