Why do newbs have such mindset "never sell their coin when it's in negative"?

You know your negatively performing coins are not going to recover because they failed at the most fundamental level,
they are meant to be just a pump and dump coin, not selling your loss just because they're in lost and hoping for a recovery is plain stupid.

You don't sell something only if you believe they are a good project from the fundamental level but experience a temporary fluctuation.

You should start from learning, then reconsider your investment strategy, here's a blog post that I share a portfolio that I believe is best for the average investor.