Partly the dynamics of this sort of thing, at least as it comes to social (especially romantic) relationships, play a big role. Using romantic as an example, traditionally, men are more expected to be direct, taking a proactive role - they're supposed to be the one who asks the woman out. Again, from a traditional standpoint, the woman isn't supposed to take direct action - instead, she's expected to drop subtle hints. (Again, this is speaking in the old/traditional sense)

The problem comes when, for whatever reason, the other party doesn't pick up on those signals (either of interest or lack thereof). It makes things a lot harder, for what should be obvious reasons. Autism can very easily lead to this sort of problem, but is hardly the only one.