In the study of economics, Investment mean any addition in physical stock as well as stock of finished goods, or you can say any putting money in anything for the motive of profit.I want to know your opinion that what are main challenges for small investors in any type of business now a days, If he/she has nothing after his investment?
Very simple. small capital = small gains, not unless you got lucky and hit a jackpot that will give your small investments big returns like x100 or even greater. That's why you really need to be aware how much you are going to invest and the potential of good returns.
However, in the equation, there is also risk, that both small and big capital had to face, because both of them can end up with nothing as well. That's why if you are going to invest with small capital, the risk can be mitigated if you are going to hold it for long term and hope to get a windfall at the end.
I think it depends the kind of business (and how professional you are). Some people can make a decent profit investing in cheap items (buying and reselling for an example), taking advantage from the quantity, while someone with more money can make less profit investing in average/expensive or not knowing what are the best items to resell, taking the less profitable ones.
Something similar can happen in Crypto world. Someone with a lower investment can make more profit choosing the right Altcoin, while someone with a higher investment can have a lower profit choosing the "wrong" AltCoin. And it can rely on luck, as you said, or on market skills of the individual.
I believe the main challenge here is to have enough skills to make a decent deal in the end without big money and being more or equally successful than the bigger investors.