Ultraviolet light degrades lightweight tent fabric (and almost any synthetic material). UV light will cause the fabric to fade, lose strength, and eventually disintegrate.
The amount of UV damage is directly related to the fabric's exposure to the sun and the altitude at which the tent is pitched. If it is left pitched during the day, high-altitude exposure can damage a tent beyond use within a month.
The best way to prolong the life of your tent is to keep it out of the sun. Pitch your tent in a shady spot whenever possible. By striking (taking your tent down) in the morning and pitching your tent late in the day, your tent will last many years.