system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why are some outlets so difficult to plug things into, while others are very loose?
gpt
Receptacles deliver power to plugs via spring clips. Everytime you plug something in or take it out, the springs take some wear and tear.  They wear out over time and are rated for x amount of timed you can plug/unplug . 

Cheaper receptacles are rated for less times while more expensive receptacles are made better/have better materials and are typically rated for a higher amount.  

*edit hospital grade receptacles have a much high spring tension
Or You might also be used tamper resistant receptacles and people have issues with the plastic guards retracting if the plug is not inserted properly.