On making design decisions - favor 'if/else' over polymorphic

In the world of object oriented programming, we tend to think everything in the way of like:

"What's shared in the two concepts?"
"What operations should be defined in the interface?"
"How should the sub classes different themselves?"
...

And forget that they can actually be done with simple 'if/else' in a few lines.
And that the 'if/else' approach seems to be most --

natural,
flexible,
scalable,
readable,
clear,
and neat.

Surprising!