When you stop learning you're dead.
Stage 1: Absorb and Process
You've decided to sell on Amazon, so now you have to learn how it all works and process the information. This stage can take 2-3 months to get a handle on things. Be patient. Read, listen, watch, learn and grow.
Stage 2: The Learning Curve
You're jumping in by scanning, listing, prepping, packing, and selling. You're making some money (or a lot of money), but you have a gazillion questions, and you're making mistakes left and right. Depending on how fast of a learner you are this stage can last 3 to 6 months (or longer).
Stage 3: The Testing Stage
You have a handle on the basics now, so you're testing theories from buying to pricing. You're trying out new categories, discovering new products, and finding little niches that makes it all worthwhile. This stage can last forever (because you can move into the next stages, yet still be in the testing stage).
Stage 4: The Lightbulb Stage
You're figuring things out, experiencing multiple a-ha moments, and reworking your plan. You get it now, but you also know that the game is ever changing and you should always strive to learn new things. This stage kicks in at different points for different people, but continues forever as long as you continue to learn and grown.
Stage 5: The Scale Up Stage
You might start this stage very early on, but the learning curve could be bigger if you scale up right out of the box. Most people take a hard look at their business, pay close attention to the date, then begin to formulate a plan to take their business to the next level. This is a forever repeatable stage.