The core but unspoken idea of socialism is a zero-sum world. Everything stems from that. Marx's labor theory of value is an attempt to explain how economy works given that premise. In a zero-sum world every profit indeed means loss for the other party; so employers' profits must come from workers exploitation.

There's no room for any improvement in this mindset. In a zero-sum world being more efficient at something and hence more profitable means you're stealing, either from customers or from less-efficient producers. Which really means any attempt at making things better is evil.

After a generation or two people start to internalize it, and you get a 'homo sovieticus' society which interprets any ambition as aggression - wanting a better life becomes synonymous with wanting to steal.