Through painful trial and error, I've found that my hunch that a woman likes me is almost always wrong. Someone will be flirting very heavily with me, and I'll think "there is no way in the world she's not into me", and then it will turn out she will not be into me.

It may also be that you are recognizing the indications of interest correctly, but then screwing things up with your follow-up behavior. Usually, female attraction in the initial phases is easy to destroy with even a single serious misstep. (And it may be serious even if it seems insignificant or altogether non-obvious to you.)