No, full rational choice theory posits that people do behave in a way which maximizes actual (not expected) net utility, or, in more detail, as if:
(1) They have a coherent “utility function” mapping each potential path through time that might be taken to a unidimensional, real-number utility value.
(2) They have perfect knowledge of the outcome (path through time), or at least resulting utility value, produced by every possible option with every decision they make,
(3) They consistently choose the option that maximizes utility.
There are more limited modifications of rational choice theory that attempt, with varying degrees of success, to close the predictive gap between full rational choice theory and actual behavior resulting from the fact that humans do not behave “rationally” in the sense of rational choice theory, but they aren't what is involved with the question “how can you lose when rationality is on your side?” asked upthread.
You could lose because the rational choice model does not accurately model human behavior in the real world; people don't act based on perfect information, in part because even when presented with correct information, they are likely to reject it if it doesn't fit their pre-existing world view.