Man X looks fucking awesome I will just sneak X in, and all is well. Suddenly Y starts to look really sexy I Will just sneak Y in, and all is well. Man Z looks really fuck im overtrained and hurt.
Balance within a program is 100% possible, but let's not forget that training is training. You are literally working on improving variables over the course of a set time period. If you add a bunch of shit then you arent training the same variables any more, are ya?
Balance is possible, but it makes way more sense to achieve Balance between subsequent program than within a single program. This isnt a new concept by any means. Even within the annuls of dinosaur training it is suggested to switch between a leg focused and back focused program. Super squats has you switch between the core 20 rep squat routine and a 5x5. Dan John outlines a clear year long routine that oscillates between easy strength, the armor building formula programs, and mass made simple. Within each program there is a small amount of movements you set out to improve.
So how can you curb the fomo? If using easy strength you lack the squat movement. Super squats lacks a heavy hinge (easy stiff leg dead only). There is an answer and it can be - mobility, conditioning. Two things everyone needs and doesnt want to do. Program weak on squats? Do a shitton of squat/duck walk mobility etc.