[barneysversion]

Reification is usually a fallacy when we take the abstraction too far. The canonical example being "the map is not the territory" where someone confuses every mark on a map with actual features of the terrain.

One could argue that abstractions "actually exist literally" without being physical. Gravitational fields don't exist physically but do exist and they're a valid abstraction that's useful to measure. Maybe happiness is a phenomenon that could be useful too (though I would say to a lesser extent.)

A little tangential but... even things that we would say exist physically are not on closer inspection. Does a chair actually exist or is it a platonic ideal that we apply to a collection of atoms assembled to form four legs, seat and a back?

[JackPoach]

You are absolutely correct. Moreover, reifications can be useful or harmful - purely based on how they are being used. That's why maps are actually useful, except for several individuals that died in Australia and other places by trusting their navigators more than their own eyes and actual surroundings. I've been in situations where GPS malfunctioned and when I quickly realized it I understood that I should not follow the map.