Someone I know trades interest rates. He gains and loses millions at a time. He absolutely knows what he is doing, and he makes a LOT of money. He says it’s just math. If only it were really so simple!
It is possible to accidentally make a wash sale when trading in a non-retirement account. A wash sale is a sale that can result in a capital loss when you also made a purchase of the same thing within a certain amount of time as the sale. In that case, the realization of the capital loss is delayed, and tax record keeping and calculations get more complicated.
https://www.irs.gov/publications/p550#en_US_2019_publink100010601