Persistent vs Annoying for cold emailing/calling

I keep reading on WSO that people email/call MD's/hiring managers multiple times even if the first two times yielded no result. When I ask for advice on cold emailing, people say "Follow up once and then let it go if you don't get a response". I'm not really sure what to follow as I want to be persistent and I feel that if I followed up 1-2 times more per person I would have gotten more responses. Any input is appreciated.