Since most of the new trader has the posibility to lose their account first avoiding large investment is the best we can do at that time.And we can trade smaller lot size so that we can trade for longer.Longer we trade on forex we get experianced and there will be more posibility to get the profit after that.So 100$ investment for new trader is very good investment. can get tradign sowell small amount if a person start tradimg with 10$ then he should must be a good forex trader and he should has a complete knowledge about forex trading if he has no knowledge about trading then he can do not trade with 100$ and he may got high loss and may be his account washed at 0 zero.