Who said anything about knowing the odds on the coin? That's irrelevant. If I know tails is more likely than heads, regardless if the edge is big or tiny, it still makes sense to bet on the most likely outcome. If I want to optimally size my bet, sure I need to know the correct probability but in terms of a straight-up bet, I just need to know the most likely outcome.
It comes down to knowing how to find trends and only trends, which admittedly most TF traders can't do. And that includes the professionals. You can find trends with a moving average crossover. But that crude tool will also find you chop, which you don't want. Finding trends while avoiding chop or minimizing damage from chop isn't easy but it's doable. Don't ask how, nobody is going to hand you such a wonderful gift. Remember: even most professionals don't know that stuff.