Why my cars gear stick popping out from 1st to 3rd gear, from 2nd to 4th?

The car is Ford Focus 2002 1.8tdci. Poppong out from 1st gear to 3rd and from 2nd to 4th. Reverse works fine, I'm able to start to drive car from 3rd gear with balancing clutch and acceleration. No strange noises thou.

The synchro has gone.
Time for a recon box.

I would guess that gears are worn in the transmission; or perhaps the shifter needs adjustment.

Gears usually jump out for three reasons, you have worn or damaged gear linkages which are the cable that run from your gear stick to gear box and select gears, another is worn synchronizer units inside this is caused by you grinding gears and is unlikely to be the cause of them all jumping out. Worn selector forks are what push the synchronizers in place and are another unlikely fault for all gears, i would expect the gear linkages have probably worn so there's too much play you are taking up before selecting gear which prevents it being selected properly the linkages themselves can be picked up from around £40 although i'm not sure how much it would cost to have them fitted.