The ventilation-insulation balance in a tent is essential for safe and comfortable camping under different weather conditions. Ventilation vs Insulation: The Tent Balance ,Ventilation and insulation are seemingly contradictory, but it is important to know how they interact with each other in order to select the proper tent and effectively manage your shelter.

Ventilation: Avoiding Condensation and Providing Airflow
Why it matters: Ventilation is the air flowing into and out of the tent. It's mostly crucial for:
Preventing condensation: Hot, damp air from your breath and body warmth can condense on the cold inner surfaces of the tent, creating wetness and unpleasantness. Ventilation lets this damp air leave.
Temperature control during hot weather: Air movement keeps the tent interior cooler by radiating heat.
Fresh air supply: Ventilation provides a steady supply of fresh air for respiration.
How tents provide ventilation:
Mesh panels: Most tents feature mesh windows, doors, and occasionally even entire inner tent walls to aid in airflow.
Vents: Rainfly vents, usually located at the top of a tent, let warm, moist air out and reduce rain ingress.
Double-wall design: The space between the inner tent and rainfly provides improved ventilation and condensation control.
Doors and windows: Ventilation is maximized by opening doors and windows (if possible weather-wise).
Ventilation management:
Direction of pitch: If it is breezy, having the tent face into the wind can enhance ventilation.
Opening windows and vents: Open all vents and partly open doors/windows, even on cold days, to control moisture.
Prevention of damp sites: Camp in areas near water sources since the humidity and condensation are high.  
Insulation: Maintaining Warmth and Keeping Out Cold
Why it matters: Insulation is the capability of the tent to withstand heat transfer. It is mostly important for:
Keeping warm in cold weather: Insulation keeps your body heat within the tent and does not allow heat to escape to the colder external air.
Keeping a moderate temperature in hot weather: Some insulation, especially reflective layers, can prevent solar heat from entering the tent.
How tents insulate (though usually minimal):
Fabric weight and layers: Thicker, heavier fabrics and multiple layers can provide a slight amount of insulation.
Four-season tents: These tents tend to have less mesh and a full rainfly that comes closer to the ground, which keeps heat in and drafts out. Some even use special insulating materials in the fabric.
"Fresh & Black" technology: Reflective coatings on the flysheet can help block sunlight and reduce heat buildup inside the tent.   
Improving tent insulation (mostly external or personal):
Sleeping bag and pad: Your primary sources of insulation for staying warm are your sleeping bag (rated for the expected temperatures) and an insulated sleeping pad (with a high R-value to prevent heat loss to the ground).
Tent footprint: Offers a insulation from the cold ground.
External coverings: Space blankets or thermal tarps over the tent can radiate some heat inwards (outwards during heat).
Internal liners: Fleece blankets placed inside the tent can retain some heat.
Smaller tent: A smaller tent contains less volume of air that needs to be heated by your body heat.
The Balancing Act:
The perfect balance between ventilation and insulation largely relies on the specific weather conditions you're expecting:

Cold Weather: Insulation takes priority to keep warm. Still, some ventilation remains important for handling condensation from your breathing. In most cases, that involves using a 4-season tent with little mesh but using the vents judiciously. Layering and having a warm sleeping bag and pad are essential.
Warm Weather: Ventilation is the key to staying cool and avoiding overheating. Tents with plenty of mesh and good airflow are best. Insulation to keep direct sunlight out (such as "Fresh & Black" technology) can also be useful.
Rainy Weather: A well-ventilated, waterproof tent is a must. You want to keep the rain out, but you also don't want excess condensation in the tent. This usually entails a balance between closed windows in the wind direction and slightly open vents/windows in the leeward direction.
Shoulder Seasons (Spring/Autumn): Conditions may be changeable. A flexible 3-season tent with adjustable ventilation capabilities is generally ideal. You'll have to be willing to layer clothing and modify ventilation as temperatures change.  
Key Takeaway:

Tents are for the most part protection from the weather (wind, rain, sun) and a measure of privacy. They have little inherent insulation. Your sleeping bag and sleeping pad are your main protection from the cold. Ventilation is an inherent characteristic of most tents, and proper control of it is essential to be comfortable and to avoid condensation in all weather.

When shopping for a tent:

Keep in mind the main climate and seasons you will be camping in.
Find a tent that has sufficient ventilation details (mesh, vents).
Inspect the waterproofing rating for precipitation expected.
Remember that insulation is primarily controlled through your sleeping gear and clothing.
By learning the relationship between ventilation and insulation, you can make informed choices in your tent and camping techniques in order to stay comfortable on most outdoor pursuits.