That's a bit of a simplified view I had my first years. Even if we leave aside equity long bias, there are actors that are buying and selling for other reasons than to have "highest return" in your selected time frame. You may effectively be providing such actors with a service (being the best party for them to transact with) and your positive expectancy can be considered the premium you are paid for that service.
Consider for instance dip buying an evening the market tanks 3% and holding until a few days later after it has recovered. In such a case you are warehousing risk some actors don't want.
I actually want to keep it simple for now, I have no intentions of winning the market. Simply want to make some money off my savings
PS I already have some safe options locked in, sparing some extra dough for trading.