You may have a friend that is busy a lot. Or doesn’t like going out that much. Or spends a lot of time with their partner, or whatever. But don’t stop asking them out, just because you expect them to say ‘NO’. Because one time, they may need your friendship, or you theirs, and that’ll be the time they accept your invitation. It’s horrible to stop being invited to things. It’s also good to invite people even if you know that they won’t be able to come – it’s a gesture and an acknowledgement of friendship.
Always ask. You never know.