Since our physical and mental resources are limited, you have to prioritize the exercises that give you the most bang for your buck and within your physical capacity. The best way to do that is to keep the routine simple.
For example, your goal is to look more fit for the summer. Most beginners would do a 30-minute jog on the treadmill, do 3 exercises for chest, do another 3 exercises for back, 3 exercises for abs, a couple sets for legs, a few bicep supersets, some tricep supersets and a plethora of other isolation movements to make sure they get that "toned" look. All those overly complicated variations will overwhelm even the most seasoned lifter.
In reality, 2 sets each of the Barbell Back Squat, Flat Dumbbell Press and Chest-supported Rows performed with good form are enough to stimulate growth for that day. Even a newbie would be willing to complete this routine multiple times a week and throw in some cardio on the rest days. Even just reading that makes you realize that there is power in simplicity.