@taxes96786 But neither 1099 nor win/loss statement determines whether an income should be reported.

1099 is only an information return that obliges the payer/withholding agent to report and withhold on an income.  Although the payee could reference the info on it for tax reporting, whether or not the payee receives a 1099 is not determinative of whether the payee must report an income or what amount should be report on the recipient's return.

Similarly, the win/loss statement is merely a document that helps determine the extent to which a loss may be deductible.

§61(a) states, in part, that "[e]xcept as otherwise provided in this subtitle, gross income means all income from whatever source derived".  As the others explained, the why is important because it determines the character of an income, whether it falls under one of the exceptions defined within the Code, or whether it should be treated as a gift governed by Subtitle B of Title 26.