If you cannot engage 100% but somewhat stuck 1/2 way before you manage to force it in (either with a bit of brute force, or manage to slide it in somewhat with a "notchy" or even gear "clashing" then you may have worn out syncho(s).
normally, a syncho, when sync' up with the gear to be mated (shifting into gear), should be smooth and one seamless action (from 0 to 100%). Anything that stops you from properly siding (engaging) the gear means your gear lube maybe at fault, or worn synchro, or both.
Q.
p.s. I'd prefer to go from 0 to 100% (from neutral straight into gear) in one single, continuous motion...and never hesitate or stop somewhere in the middle. Also: once engaged into gear, your shift stick should stay in position. If you have a poor habit of laying your hand on the shifter stick, you may (over time) wear out the gear detention spring or checkball, which will cause the stick to jump out of gear.