can not mirror this

I tried to mirror this :
Shift + D then esc then CTRL+M then X but nothing happens??.

This is the blend file:

I don’t know why it doesn’t mirror, but it works if you put the new object into edit mode (tab) and then select all vertices, then mirror.

By the way, mirroring like that will leave you with two separate objects which you will have to join together afterwards. It could be better to use the mirror modifier - you can have it join vertices that are on the mirror line, and when you’re done modelling you can click “apply” to make it real.

In edit mode, thanks. should it be also work in object mode ?

I found it under modifiers - add mirror .

All modifiers live in a menu in the editing context (F9). There’s a panel called “modifiers”. Click the button “add modifier” and choose “mirror”. You can select the axis to mirror on, and if you select “Do Clipping” then any vertices on the mirror axis get locked there and merged with those of the mirror image. Note that the clipping part is designed to be used while modelling, so if you use it on something that’s already been modelled like your man here, you have to just select all the verts and move them towards or away from the mirror axis until the clipping grabs them - just play with it and you’ll see what I mean, hopefully.

Thanks for the explanation.
The clipping part is designed to be used while modelling any vertices on the mirror axis get locked, can I use this only once?
Oke I will play with it but at the moment I am on my work.

F9 in edit mode is not working for me .
Modifiers mirror works great but clipping did not remove double vertices for me.

Mhh I have a strange line in the middle of the body. Does not look good. What did I do wrong. Still find mirror very hard to do with my character.