Why you cannot maximize both
Volume, the total amount of work, and intensity, how heavy each effort is relative to maximum, both drive adaptation, but they draw on the same finite recovery budget. Pushing one hard generally forces the other down: very heavy sessions cannot also be high in total reps without accumulating unsustainable fatigue, and high-volume work cannot all be done at near-maximal loads. This trade-off is a fundamental constraint that periodization is built to manage.
It is why programs cycle their emphasis rather than chasing maximal volume and maximal intensity at the same time.
How periodization exploits it
Models such as linear, block, and undulating periodization all amount to deciding when to favor volume and when to favor intensity. Early phases often emphasize volume to build capacity and muscle; later phases shift toward intensity to express strength, with the trade-off guiding the hand-off.
An organizing principle
Where exactly to sit on the volume-intensity scale depends on the goal, training age, and recovery capacity, so the balance is individual. This is general educational information about training, not medical advice.