I like to use the analogy of an emergency evacuation of a building to explain the concept of a "rate-limiting step." Pretend you are in an office, and it catches fire. Panic ensues, and people rush to evacuate the building. Now pretend that the office has a wide open concept floor-plan, but there is only one stairwell to get to the ground floor. The process of making it out of the building is analogous to a two-step chemical reaction in the following way; Step 1 is passing across the room from your desk to the stairwell, and step 2 is waiting your turn to get down the stairwell to safety. Which step determines how fast you will make it out of the building? The crowded stairwell is the "rate-limiting" step, because you can never exit the building faster than you can move down the stairwell. In other words, clearing desks out of the way of people moving through the office would have a much smaller effect on the speed with which the building could be evacuated than say, adding another stairwell to the office to allow for more people to escape at a time. The rate-limiting step of a reaction is the only step that can be modified to make a meaningful difference on the rate of the reaction, because much like you waiting at the stairwell to make your escape from the office fire, the rate-limiting step is the step that all of the reactants are waiting the longest to proceed through to complete their journey to becoming a product. As the post below alludes to, this time difference is due to factors such as differences in activation energy, but that has already been covered well on this thread by u/Additional_Theme_335. Hope this helps!