It all depends on the expertise skills and affordability along with luck. There are users who profit big in the very first trading. This is just about the 75% of luck and 25% on the predictions. So invest with small amounts will help know more about trading and even if lost during the process this won't affect in the larger scale.
I don't think that the word luck is belong to trading because trading is not that based on luck, it is based on hypes, analysis and also knowledge. If you know how to ride the hypes then you can make profit in trading, if you know how to analyze the market based on the given informations then you can make profit and last but not the least, if you have enough knowledge to combine all the things up then you can have a limitless profit.