Once upon a time, there was a cell. It was moving around the primordial soup trying to make it in that harsh world. All of a sudden, it encountered a small prokaryotic cell. To be honest, the cell was feeling a little lonely and it was happy to come across somebody to share the habitat with. The two cells started spending a lot of time together, just quietly coexisting. The first cell started thinking how it would be so much easier to survive if the other, small cell were to live with me. I could provide safety and shelter, and the small cell can pay me back by providing me with the energy I need for my daily metabolic processes. The cell was hesitant for a second, but then bravely said ''Hey, what do you think about symbiosis?''. And the rest is (endosymbiotic) history.
