Lancair ES pilot reported the main cabin door departed the aircraft in flight; likely because it was improperly latched.

Narrative

Door departed aircraft while climbing to 3000 ft. I closed it and heard the over-center link click; but I don't think the hooks grabbed the pins. Visual evidence after landing confirms this; as the hooks took some of the paint away; and it appears from what I've seen of the door (found in a field) that the mechanism was down and latched. But I think the hooks grabbed the fuselage rather than the pins; which are still in place (rock solid); and that wasn't strong enough to hold the door given the low pressure on the outside of the skin when at speed. The door was gone all of a sudden--it just flew off. Appears it didn't hit anything. I was in the soup; so it was a little unnerving; but excellent training made it somewhat routine. I executed an instrument approach back to ZZZ and am diagnosing today. I think I've probably got it right.To give myself a little break (though I think it's on me). I had just had the condition inspection. We lubed the door mechanism and it was operating very smoothly as a result. I thought 'wow; this is great.' But the change in tactile response to the over-center link closing and locking might have contributed to me missing that the hooks did not grab the pins (I think...I don't know this for sure; but it is what I think happened). The lesson is to always check that there is zero play in the door after the latch is closed. I certainly will after I get the door rebuilt and reinstalled.