Why does my staircase look that undetailed normally but when pressing "Tab" it's fix?

[DanielNL]

See here:

first after importing my .obj, I am shocked my staircase got “destroyed”:

After pressing “Tab”, it all seems fixed? all faces showing up suddenly?

Can sb. explain why it looks so “destroyed” in the first picture?

[kwikker]

It might be smooth shaded

It can be changed in 3dView (T) panel

[Richard_Marklew]

Why have you failed to supply any demo blend file that demonstrates the issue. This is mandatory for all support questions.

Clear any custom split normal data if you have imported any

Recalculate selected face normals (Ctrl+N)