do a man effect the foreign market

When I was Senior High school until now in university, on economic faculty, the teachers tell me that no one can effect foreign exchange market (forex). In economic theory, appreciation and depreciation is an indicators of foreign market. no one can effect the market, but if there so many people or quantity of money to buy or sell a currency appreciation and depreciation will cause the currency. in other word. if dollar was hold by many people and high in nominal, we can say dollar will appreciate.

back in topic, what will see now? Indonesian believe that only one George Soros effect fallen Rupiah in 1998. (Sorros declines this statement later). in other example, recent years ago, he won 1 million dollar and destroy bank of england.

from this example above, I know that my teachers goes wrong. one man can cause the appreciation and depreciation a currency. but the same assumption from the teachers and me are equal. Sorros can do that because he has much money. and economic theory assumption that rich man don't allocate their whole money in speculation.