First, good traders don't try to maximize the odds of winning. They look maximize their profits within the context of the kind of risk they are willing to accept. Odds of winning is only part of that equation.
Second, you need to define what you mean by "risk" in the context of your discussion because at least for me it isn't clear.
Third, you need to identify which variables you are talking about that are not constant and indicate whether you are talking about just for a given trade or for you whole trading experience (or some other segment of time).
Beyond that, I think most traders would argue that they actually do look to "quantize" their risks in that they define what they are willing to lose on a given position and/or over a given period of time.
Also, to say that trade holding periods are random is not correct. They may be random within a constrained range of outcomes (for example, a day trader will not hold any position beyond the end of the day), but that isn't the same as truly random. Even if you aren't fully constrained as a day trader is, any given trade has a likely range of potential holding periods based on the exit conditions defined by the trader's strategy.
And beyond that, suggesting traders do not take time into consideration in their trades is incorrect. Many do in the shape of "If the market doesn't do X with Y amount of time I will exit".
If you define risk in terms of the size of a loss suffered should the market go against you, then you are correct. There are only two ways to reduce that risk - smaller trades and shorter holding periods. Not losing on any trade at all is not a third option because there's no chance of losing any sized amount no matter what you do.
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