When a person hits that subscribe button they are saying, I want this person's content... not I want you @Youtube to decide what portion of content I get.... C'mon guys, to subscribe is an action, which means that sub is saying, give me this content
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If a subscriber pushes the bell, they opt in to all notifications for that channel. Regardless of how much they actively view it. Those who HAVEN'T pushed the bell, but are very active with a channel will occasionally get one as well. Hope this clears it uppic.twitter.com/rZkJNEkPbS