As teenagers we learned the hard way that if you contact someone and they don’t reply, they’re just not into you. If you keep trying, you must be a total loser.
But in the business world, it’s the opposite. If you don’t keep trying, you’re a loser.
If someone doesn’t reply to you, it probably wasn’t intentional. If you try only once, then take it personally, and forever assume they’re a jerk, that’s actually quite rude of you.
It’s more polite to contact them until they reply.
It shows that you understand that everyone is busy, and their situation has nothing to do with you.