To understand and appreciate the forex market's size, perhaps it would help to review the daily turnover of the past years.
If we go back in time and more specifically to the year 2001, the daily turnover was roughly above 1 trillion US Dollars.
Since then, a lot has changed, and as a result, many more traders have joined the foreign exchange market, with the corresponding daily turnover to be skyrocketing.

That is quite impressive, I have to admit, if you consider that the major exchanges are measured in billions!
The next available statistics follow an uptrend in daily turnover.
More precisely, in 2004, the daily turnover was just below 2 trillion; in 2007, it was roughly above 3 trillion US dollars; in 2010, it almost reached 4 trillion, whereas in 2013 and 2016, the daily turnover was close to 5 trillion.
The latest available statistics for the year 2019 find the daily turnover above 6 trillion US Dollars.

These numbers ensure that one trader alone cannot manipulate this market, and additionally, traders may enter buy and sell transactions without worrying whether their orders will be executed or not.

Additionally, it provides awesome opportunities for traders around the world who want to take advantage and potentially profit from price fluctuations.