Explain
Osmosis in terms of a busy Tube carriage
Osmosis is just a crowded Central Line carriage where the water molecules are the commuters frantically trying to squeeze into the space that has fewer people.
In this scenario, the semi-permeable membrane is the sliding door of the carriage, and the salt particles are the stubborn tourists with massive rucksacks who are far too bulky to fit through the gap. The water molecules move randomly, bouncing off the doors and the adverts for laser hair removal, drifting from the dilute side with plenty of standing room into the concentrated side that is already packed with commuters clutching lukewarm meal deals. They are desperate for a bit of space, but the rucksack-toting salt ions act like unmovable obstacles, effectively hogging the floor space and stopping the water from ever truly balancing out the environment.
This frantic shifting continues because the water molecules have no sense of direction or social hierarchy, they just happen to bounce through the gaps until the pressure from the already-squashed commuters makes further movement impossible. It is not a calculated choice to relocate for a better commute; it is purely the result of water molecules rattling around like teenagers on a Friday night, unaware that they are participating in a fundamental biological process. Eventually, the density of the packed commuters matches the sparse ones, and the frantic shuffling stops, leaving everyone exactly where they were destined to be: uncomfortable, stationary, and waiting for the next stop.
Where the analogy breaks downCommuters have legs and a basic desire to not be crushed, whereas water molecules are just mindlessly vibrating particles.