Sometimes a guy will be able to talk to someone he's interested in, often because the circumstances put them together, so the onus wasn't on him to approach anyone.If they like someone they'll often feel too nervous to ask them out and face the awkwardness and risk of rejection that entails.
Sometimes they just won't get nervous around someone for whatever mysterious reason.
He notices she seems like she's becoming attracted to him, and he blows things soon after.
Hanging out, going on a date, the idea is the same.
They may never ask them out, or put it off so long that by the time they do they're well into the Friend Zone.
Even with all of the above stacked against them, a shyer, inexperienced guy will sometimes have enough things go their way that they end up in a position where they're alone with a woman and want to 'make a move' on them (e.g., kiss them, put their arm around them, etc.).