CONSTRAINT DRIVES DESIGN.
If necessity is the mother of invention, then constraint is the daddy of design. Constraint might sound like a dirty word (maybe moreso after that last sentence), but it’s often productive to look for and understand your constraints, and work with these to help focus your design. Constraints are commonly technical - for example mobile phones don’t have powerful GPUs - and design decisions are often directed by them - low-poly art is one solution that can look “good”, without stressing low spec devices.
Of course constraints come in other forms. Doom has a limited set of mechanics, a limited set of weapons, a limited set of enemies. I want exploring the level to be exciting, with something new around every corner. I want each enemy encounter to be varied, with a different opportunity to die around every corner. The straightforward solution might be to add new weapons or enemy types - which is technically feasible with the modern Doom sourceports - but choosing to work within Doom’s constraints have forced me to come up with creative solutions and to work hard and get the most out of the few mechanics available.
The flipside to understanding your constraints is that you also understand your freedom. Yes, I want variety in enemy encounters, and while I may not have freedom over weapon or enemy types, I do have freedom to control enemy placement and combination, the design of the environment, the order that weapons can be collected, and even the health or state of mind, or expectation of the player.
There is a quote - “perfection is achieved not when there is nothing more to add, but when there is nothing left to take away” - that rings true here. Understanding your constraints - or setting your own - helps you think hard and really make the most out of what you already have, rather than jumping straight to solutions involving new mechanics or content.