Left Drag ratio?
The simple answer is your average light airplane weighs around 3000 lbs, therefore needs 3000lbs of lift.
However, it DOES NOT have 3000lbs of drag, therefore does not need 3000lbs of thrust.
Enter the L/D ratio, which for a half decent airplane is aroundabout 10/1, with the usual variables of manufacturer, flap deployment and all that other rubbish.
So, if your AFM says your L/D ratio is 10/1, and you weigh 3000lbs, your thrust and drag components are 300 lbs each, in S&L flight, and that is why the four forces are not equal to each other.