+1, it was misalignment of the pin during installation. The end of the pin is square, so if it hits the side of the hole it doesn't self align the way a pointed pin would.

Next time, as you press the pin try to feel the change in pressure as it comes to the far plate, then make sure the chain is aligned before pressing farther. It helps to not have to fight tension, so consider dropping the chain off the inner ring onto the BB shell. Now use touch to judge if the pin is entering the hole, or pressing on the side of it. Sometimes you have to kinda of flex things to help it find the hole and slide in.

Since installing a chain usually means you've removed one, use the old chain for practice until you can tell by feel alone whether the pin is sliding in correctly or hanging up.


BTW- important-, Most modern chains cannot be securely closed with a chain tool. They depend on the rivets being peened over the plates to keep from spreading and breaking during hard shifts. So if this is a 7s (some), 8s, 9s or 10s chain, you should only be cutting it with the chain tool, and closing it with a connector link, or special pin a la Campy and Shimano. If in doubt read the chains package enclosure for info about splicing.